The Fish-In Cycle

What are you doing?! Oh, the humanity of it all! Your poor, poor fish.

Ok, enough with the theatrics, you drama queen! So, you’ve been told that fish-in cycling is the wave of the future, or you just learned about cycling after having jumped the gun and purchased your tank and fish. Now what? Well, wipe away your tears, dear friend, because there’s hope for you yet!

Fish-in cycling has been used for many years as a viable means to growing beneficial bacteria. In fact, it’s been used ever since Nitrosomonas europaea and Nitrobacter had been discovered and believed to be the natural remedy to toxins in fresh/salt water, as these bacterias oxydize/eat Ammonia and Nitrite – Ammonia, being the waste product of fish and decaying plant/organic matter; Nitrite being the byproduct of oxidized Ammonia. Of course, that theory had been dispelled in 1998 and 2001 by Marine Biologist Dr. Timothy Hovanec, Ph.D. While this process does, indeed, occur, the true culprits, as I’ve mentioned previously, are the Ammonia oxidizing Nitrosomonas marina and Nitrite oxidizing Nitrospira bacterias.

Since fishless cycling had been devised, fish-in cycling has steadily become a thing of the past. Not only is it unnecessary, but it can take much longer to cycle your tank with fish, and it’s also harmful to your fish, thus arguably unethical.

Many local fish stores and big box stores, like Petco or Petsmart, still continue to tell consumers about fish-in cycling, merely because that’s what they had learned as aquarists from years long gone. Fresh in their minds are the days when they were told, as novices, how to use feeder Goldfish or top dwelling fish, like Danios or Mollies, to cycle their tanks. In fact, many of these stores will loan you these “cycle fish.” If any are still alive at the end of the cycle, they tell you that you can bring them back to the store for a refund or in-store credit toward one of your mainstays.

You can’t really fault them for it, because that’s the method they grew up knowing and using… they’re merely passing on their age-old knowledge to up-and-comers like yourself. Of course, you can fault them for not keeping up with the times and knowing their trade. As you’d expect a doctor to keep up on their knowledge of modern treatments, you’d expect an aquarist to keep up on their knowledge of best fish keeping practices. Maybe that’s just wishful thinking. Anyway…

On to the point!

Alright, alright… relax already. As I did for the fishless cycling methods, I’ll lay out the steps needed to fish-in cycle your aquarium via numerical order. We like to keep things simple around here… and by “we” I mean “I.” Onto the goods!

Step 1: Purchase your aquarium, filter, heater, thermometer, substrate, any decorations you’d want (including plants), dechlorinator (ie – Flourish Prime), API’s Freshwater (or Saltwater – depends on your needs) Master Test Kit, and last, but certainly not least, the fish you want to start out with.
– When you’re fish-in cycling, you don’t want to start with too many fish. You’ll want to start with about 3 (depending on the size of your tank). Any more and you’re just asking for trouble.
– When I say “fish,” I don’t mean Neons or Zebra Danios in a 55gal tank. I’m talking maybe 3 Serpae Tetras (or Feeder Goldfish) in a 10-40 gallon tank. Possibly 5-7 in a 40-75 gallon tank. Use your best judgement for 90+ gallons. And since you’ll be doing your best to keep these fish in good health, try choosing fish you want to keep.

Step 2: Rinse your filter out with cold running tap water and fill it with sponge media (which is the mechanical filtration) and bio-media (which is your biological filtration – this is where your BB colony will grow). Your sponge can, however, hold a good amount of BB, as well. This media is all you’ll need. You won’t need anything else, including carbon (which is chemical filtration), ammonia-eating filtration that can be purchased (this defeats the purpose and won’t last forever), or anything else that isn’t a sponge or bio-media.

Step 3: Fill your aquarium with tap water, add dechlorinator, and add your substrate and decor.

Step 4: Raise the temperature of your heater to 82′F. You can keep it at your regular temp for your fish (say 79’F), but raising the temperature will create an optimal environment for growing your BB colony. They enjoy warmer temps and your fish won’t mind the temporary temperature increase.

Step 5: Acclimate your fish to your tank. You can either do this via drip method or bag method. The bag method requires you to keep the fish (while in the bag they came in) floating in the tank water for about 10-15 minutes. This is usually acceptable if you purchased your fish from a local fish store, which more than likely has the same quality of water that you do at your home. If your water differs from your fish store, or you mail ordered your fish, then drip acclimate your fish in a bucket for about 1-3 hours. Click here for more information on drip acclimation. Once acclimated to your water’s parameters and temperature, add your fish to the tank.

Step 6: With your Master Test Kit, you’re going to need to test for Ammonia every 24 hours, especially since you’ll be feeding your fish on a daily basis (possibly 2-3 times per day – I would suggest once a day or very small portions 2-3 times a day). Fish waste, including uneaten food will contribute to your Ammonia buildup. Ammonia is obviously the toxin that will harm and can cause death via Ammonia burn.

Step 7: Once you begin to see Ammonia, you need to watch it like a hawk. You want to keep the Ammonia at tolerable levels for the fish, which is <=.25ppm. That means, if you see Ammonia rise to .5ppm or higher, you'll need to do a water change - it's normal that the level can surpass .5ppm (be weary of it). Since this will be a daily/bi-daily occurrence, you may need to do daily/bi-daily water changes to keep the Ammonia low. Remember: ALWAYS use dechlorinator when adding new water to your tank. If you’re adding the water from a bucket, add the dechlorinator to the bucket. If via siphon, turn off your filter, add dechlorinator to the tank (enough for the entire tank), and then add your water. Only then should you turn on your filter again.

Step 8: Continue to test for Ammonia on a daily basis, while doing your water changes. If your Ammonia levels seem to be going down a bit (ie – you’re no longer reaching 1ppm or .5ppm every day), start testing for Nitrites. It can take a week or more until you finally see Nitrites building. Be patient. Fish-in cycling takes a lot longer than fishless cycling.

Step 9: Continue to test for Ammonia and Nitrites on a daily basis, while doing your water changes. Nitrites are also a toxic compound and you’ll need to continue doing water changes to keep these at tolerable levels. Tolerable is probably .25-.5ppm, but you’ll always want to aim for 0. So do your water changes to keep your levels down.

Step 10: Once you’ve gotten a reading of 0 Ammonia and 0 Nitrites, you’ll have cycled your tank. This can take several weeks or more. Sometimes it’ll take a couple of months to reach this point. Test your water for Nitrates. If you’ve kept up with your water changes, you should have a reading of about 20ppm Nitrates. It could be lower/higher. You’ll want to do one more water change to get those down to <=10ppm. Finally: It’s about time! After weeks (maybe months) of tumultuous and trying water changes and constant testing, you’ve finally done it! Give thanks to God and bask in the glorious, brightly shining light of victory!

You’ve now grown your beneficial bacteria colony in your biological filter media for the amount of bio-load/stock you currently have. If you should want to add fish later, wait about a week, then add 2-3 more (you could get away with more in larger tanks). You’ll want to add about 3 more fish every other week, so that your beneficial bacteria has time to grow their colony and adapt to the new bio-load.

Once again, if you have any questions, please feel free to ask!

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63 thoughts on “The Fish-In Cycle

    • Hey Fergus,

      Thanks for stopping by. I’m glad I could help someone out, out there. If you have any questions, just let me know.


  1. Hey, just a quick question, maybe you said it already, but how big of a change should we do when the ammonia gets high?


    • Hi Berlin,

      When you’re doing a fish-in cycle, you don’t want the ammonia to get above .25ppm. when it reaches that amount, you’ll want to do at least a 50% pwc (partial water change). Sometimes it can take more. You should feel comfortable doing a 75% pwc if you need to, or multiple water changes to get that ammonia down. The grand majority of your beneficial bacteria will be found in your filter, so you won’t lose any of that, doing these water changes.

      Thanks for stopping by and thanks for asking that question,

  2. Pingback: Another cycling question - Newt and Salamander Forum

  3. hey so i have a 13 gal tank thats been up and running for a week now, im wanting to put my betta in it. he was left with us in a 1 gal “tank” feel bad for him… if i put him into the 13 gal and just do a 25% water change every day should he be ok?

    • He should be more than ok in the 13gal, especially if he’s the only fish in the tank.

      I assume that since you’re posting here, the tank isn’t cycled and you’ll be cycling with the Betta?

      Do you have a water test kit to test for ammonia, nitrites and nitrates?

      25% daily would be fine, but might be daunting. Just keep an eye on the ammonia levels and keep them under .25ppm. That should be a fairly simple task with just a Betta. You might only need to change the water every other day… it might be longer than that. Just keep an eye on the params so you get a feel for what you actually need to do. There’s no need to go overboard.

  4. Hi, I’ve got a 48 gal tank which has been running for 3 weeks. I bought it second hand so am using the gravel and filter which the previous owner used. It had not been running for 4 weeks when I bought it. I have been doing daily water tests for ammonia, nitrite and nitrate and still have readings of 0 on all three. I’ve got 8 danios in it which have been in for just over 2 weeks. Can you tell me how long the cycle is meant to take and when I should expect to see the values rising? Does the fact that I’m using second-hand equipment impact on the bacteria I would have initially started with? I’ve also added to the water API quick start when I first filled the tank and with subsequent water changes.

    • Hi Amalie,

      Thanks for stopping by. =]

      The bigger the tank, the longer it’s likely to take. A 48gal tank, if doing fish-in, can take up to a couple of months to cycle. Possibly shorter… possibly longer – every cycle is different.

      The reason bigger tanks take longer, is because the waste is diluted in the larger volume of water, so it takes a much longer time for ammonia to build to a noticeable level.

      8 danios, depending on the specie of danio, will likely contribute very little to the bioload in your tank, so it will take much longer to build up the waste necessary to cycle your tank.

      If they’re zebra danios, they’ll max out at about 2″ in length, full grown. I imagine you purchased them at about 1″ or so, so their bioload at this point is probably even smaller.

      Using second-hand equipment and substrate will not influence your cycle. The tank you purchased had not been running for 4 weeks, so unfortunately any bacteria that the previous owner had built would have been killed off from lack of water and food. So, essentially, you’re starting from scratch.

      When cycling my tanks, I’ve used Quick Start and I’ve gone without it. I hadn’t seen a change/benefit either way… You can continue using it, but I honestly don’t think it effects the speed at which your cycle will begin and complete.

      I would recommend purchasing Seachem Prime. It’s a dechlorinating agent that takes care of chlorine and chloramines, but it also dissipates the effects of Ammonia, converting them into a less harmful form of ammonia. This form of ammonia is less harmful to fish, but still ably consumed by the bacteria you’re trying to grow.

      You wouldn’t need to use Prime all the time, just during water changes and whenever you notice a spike in ammonia.

      Hope that helps,


  5. When water changing a 90l tank i intend to remove the required amount (10%/15%) via a siphon, then replacing the amount of water (treated) with some of the water from an electric kettle to bring the bucket up to the same temperature as the aquarium.
    Hopefully this would be less of a shock to the fish.
    Is this a good idea or should the water be cold?

    • Hey Evan,

      Thanks for stopping by. =]

      It’s a great idea to attempt to match temperatures of your tank to the replacement water you’ll be adding to it. If you get it within 1-2 degrees, you’ll be fine, but adding colder water is preferable to warmer water.

      If you add water that is warmer than your tank, you actually risk gas bubble disease, which is very rare, but it could cause problems for your fish, including death. So, if you know you’re adding water that’s a little warmer than your tank, make certain to keep your filter running to oxygenate the tank, or add a bubbler. This seems to help.

      Otherwise, adding colder water can actually simulate the addition of natural rain water, as rain water is cooler than most bodies of water. This can actually stimulate your fish and set them into breeding/mating behavior.

      I’ve found that they often enjoy a sudden rush of cool water, so I try to keep the water about 1-2 degrees cooler than the tank. You’ll notice the fish actually appreciate it.


  6. hi, i need some advice on platys.
    i have female redwag platys.
    the fins on this species have a clear sort of membrane with black “eye lash” like stripes/spines within it. (their tails are similar membrane with finer black stripes).
    on two of the fish there is a gap between the black stripes/spines. there does not appear to be any damage or nip marks to the membrane.
    is this normal?

    • I’d have to see some photos to understand what you’re describing. There are several mutations that can occur (which might be natural or not) with breeding (such as lyretails, colors, etc.). Can you provide any pictures so that I can take a look?

    • 1ppm ammonia is actually very toxic to fish. When you’re cycling your tank, you need that ammonia reading to be below .25ppm as often as possible. So, when you’re taking your readings and you see .25ppm, you need to do a water change.

      For now, I would do a very large water change (it will not effect your biological bacteria colonies) to get that ammonia down to an acceptable level. Strive for 0ppm in the tank. Your fish will constantly be providing ammonia to the biological bacteria, so any remnants that isn’t eaten right away will be registered in your testing.

      Once you reach less than .25ppm in your tank, you’ll probably need to continue your water changes at least once per day to keep the levels low.

  7. I am cycling trying to cycle an 8.5 gallon aquarium with two male guppies. Water temperature is at 80F, hardness is 20gH, and pH is 7.5. I am using Stability, API’s dechlorinator, and I did add some aquarium salt a day before I put in the fish to get the hardness where I wanted it.

    How long will it take for the ammonia spike to occur, on average? I haven’t seen one yet, and it has been 5 days.

    • Hey Lauren, thanks for stopping by! Sorry for the delay in getting to your comment – life’s been pretty busy lately. I did notice that you posted below, so I’ll respond to that one. =]


  8. I am trying to cycle an 8.5 gallon freshwater aquarium. Water parameters are as follows: Temp 80F, pH 7.5, 20gH. The aquarium water was set up on July 9th with Stability, API Tap Water Conditioner, and aquarium salt all per the package instructions and two guppies. (I want to keep endler livebearers once it is established, so the guppies are fish I intent to keep.) I have been feeding the fish two very small meals a day.

    I am currently measuring the ammonia in the tank via the SeaChem ammonia indicator. It has not detected any free ammonia in the tank.

    I thought I would see an ammonia spike by now, but I have not. Should I test for ammonia with my kit, instead of with the indicator? On average how long does it take for the ammonia spike to occur in such a small tank?

    Thank you for your help.

    • Hey there!

      Once again, I apologize for not seeing this sooner. I’m hopeful that you’ve seen some ammonia by now and you’ve started conducting water changes.

      The reason for the laxie-daisy ammonia spike, is probably due to the size and bioload of your guppies. They’re generally very low-bioload fish (until they start procreating like rabbits). While there would most definitely be ammonia in your tank after you added them, the buildup would be quite slow and your indicator probably wouldn’t be set off for several days.

      The best way to test for ammonia, however, is to use a liquid test kit, such as the one found in the API Freshwater Master Test Kit (which I recommend to most anyone taking up fishkeeping). This will be able to give you results anywhere from 0-8ppm. Much more accurate than one of those paper test strips or the ammonia indicator you’re referencing.

      Hope that helps and if you need anything else, please don’t hesitate to ask!

      Take care,

  9. This is an awesome and informational site! I am working on cycling a 36 gallon tank with 10 fish in it. I have been at it for 20 days. Been doing almost daily pwc to keep ammonia levels low. Can’t seem to get them under .50, even with 40-50% changes, but realize my API test also reads ammonium. My tap water reads (I guess ammonia/ammonium) at somewhere between .50 and 1.0! Knowing this, should I just keep doing a daily pwc whenever I get a .5 reading (which is what it seems to be every morning)? Thus far nitrites show 0, so apparently I haven’t reached that phase. FYI, I did get a Seachems ammonia test that reads both the free and total ammonia separately. It’s a little hard to use, but assuming I did it correctly, my free ammonia shows 0. I guess that is good, but will it keep the tank from cycling?

    • Wow, Brenda, thank you for the awesome complement. It’s very much appreciated. =]

      I know just what you’re going through, because a while back, our city water had an ammonium reading of about .25-.5ppm. This is actually normal for some city water, believe it or not, because Ammonia is sometimes used, jointly with Chlorine, to create Chloramines. The reason for this, is similar to just adding Chlorine, as an anti-bacterial/anti-protozoan agent, but Chloramines actually last longer throughout the water line than Chlorine does.

      This is especially troubling, of course, because Chloramines are just as harmful to our fish and biological bacteria as Chlorine is, but you’re likely to have a higher concentration, since Chlorine will dissipate more quickly with time.

      Anyway, none of this really matters to your fish or filter, if you use a good dechlorinator, which attacks everything, such as Prime/Safe.

      That being said, the total ammonia you’re detecting with your test is actually a biproduct of that chemical equation… and is actually ammonium. That’s good news, because it’s not toxic to your fish, BUT your biological filter will still consume it.

      So, knowing that you’re getting an additional .5ppm of ammonia from your tap, you can use that as a control. Not only are your fish going to be adding ammonia to the tank, but your tap water will, as well.

      Just keep that in mind, whenever you conduct your tests. If you start with .5ppm on the day of your water change and you have .5ppm in 2-3 days (instead of say .75ppm), then you do have bacteria that is eating ammonia. Otherwise, if you have .75ppm, you know that your fish have added .25ppm ammonia to the tank. At that point, I would conduct a water change.

      I would suggest you experiment a little and take your ammonia readings every day, until you have a good idea what your fish are producing on a regular basis and know how often you’ll need to conduct water changes.

      Hope that helps and again (again), sorry for the delay in getting back to you!

      Keep in touch and let us know how you’re doing.


      • I came here after searching for a step-by-step guide to fish-in cycling. What you’ve outlined on this page is precisely what I needed.

        But the best part was finding the answer to this particular question because I, too, have tap water that reads .5ppm every day.

        So I just want to say a double thanks to you! I’ll follow your steps and hopefully meet with positive results.

        • Thanks for stopping by and I’m very please that this page was able to help you (twice)! Excellent news!

          And you’re welcome. =]


  10. Hello Kevin. I am setting up a 120 gallon Discus tank. I was going to use the ammonia method to cycle tank , then was talked into using quick start by API. I now want to use the ammonia method. Can I just start over or change water and clean filters?

    • Once again… sorry for the late response. Life’s getting crazy on me.

      Congrats on an excellent choice of fish! I’m sure that 120gal will be an amazing sight to see.

      Ok, Discus are tricky and it just depends on what your goals are. For one, I’m raising 6 Discus in a 40gal Breeder right now. I bought them at about 2.25-2.5″ and want to grow them out to about 5-5.5″. Since that’s the case, I’ve been doing a lot of water changes. I started out doing daily 80% water changes. Then moved to bi-daily 80% pwcs with alternating 10% syphons to get the gunk out of there.

      As of this moment, I’ve been doing about 60% water changes every other day… sometimes I let it go for a few days or more, etc. However, I’ve added a ton of plants to this tank to keep it as healthy as I could.

      Now, I did start cycling this tank with ammonia, before I got them, but I didn’t finish the cycle. Since I was going to be doing massive water changes daily/bi-daily, it didn’t matter. Why? Because the bacteria colonies would develop over time and these massive water changes wouldn’t allow for ammonia/nitrites to build up to toxic levels.

      My question to you would be: how big are the Discus your getting and what is your goal?

      If you’re getting fully mature, adult Discus, then I would suggest you use Ammonia to build your bacteria colonies. Do not rely on API Quick Start. That’s a gimmick. Quick Start won’t harm anything, so you can just start off where you left off.

      Of course, this info is getting to you late, so you’re probably already cycled and ready to go. lol

      Hope that helps the next guy. =]

      Thanks for stopping by,

  11. Hi I have a 15 Gallon tank and I am about to start it. I am willing to have 2 dwarf gourami’s and a small pleco later. But this tank cycle is confusing me and I dont wanna buy Gouramis and risk their lives. Can I buy 3 zebra danios and get my tank cycled in 2-3 weeks?
    Please remember, I can’t buy test kits as they cost a lot in my country. I just wanna do everything naturally. Thanks in advance. 🙂

    • Hi Amit,

      Thanks for stopping by. =]

      If you have access to ammonia, I would go that route. It’s faster and you won’t have to make any fish sacrifices. Otherwise, you can use a raw shrimp that you can buy at the store/market, or you can use flake food and toss some of that in there. It doesn’t matter which way you go about it, you’ll end up with the same results. These things will rot, creating ammonia, thus starting and eventually finishing the cycle.

      Not having a test kit gets really tricky, because there’s no way to see how safe your water actually is. Knowing that I wouldn’t be able to use a kit, I would probably utilize live plants and keep the tank as heavily planted as possible.

      The best plants to use, I’ve found, are floating plants. Duckweed, Amazon Frogbit, Watter Lettuce, Hornwort, Water Sprite, etc. are all great options, as they’ll eat up Ammonia and Nitrates in great amounts. In fact, if you heavily plant your tank and utilize at least some of these, you’ll probably never have to worry about cycling the tank. It’ll eventually cycle naturally, as bacteria will grow much more slowly, but it will grow.

      Using these heavy-eating plants, you could safely add fish without cycling. It’ll take about a week for the plants to acclimate to the water conditions, so keep that in mind, when you decide to stock.

      Here’s what I’d do:
      1. Add plants
      2. Purchase some liquid fertilizer (such as Flourish Comprehensive Supplement or something similar).
      3. Dose your tank 1-2 times a week (depending on how many plants you start out with)
      4. After a week, add your livestock

      Your plants should be acclimated at that point and will begin consuming nutrients from the water column (including ammonia/nitrites/nitrates).

      In the beginning, I’d probably do bi-daily water changes of 50+%, eventually tapering that down to 30-50+% weekly changes. The bi-dailies might not be needed, due to your limited stock, but it’s better to be safe than sorry.

      Hope that helps and good luck!


  12. Hi! I just wanted to ask, cuz I have a betta which i kept for 2 wks in a 1g fish bowl (with heater, no filter, 20% water change 2x a week). Though i know that its not ideal, he seemed really happy and active. I grew very fond of him so I decided to move him in a 5g tank. What i did was I moved everything (all water and decor heater etc) from bowl to tank and just added 20% water, trying not to shock him cuz i know moving stresses the fish (his name is CHOWDER by the way :p) So now the tank’s water is just 1/4 of the tank. Can i just keep adding 20% water daily till its full? Will this shock my fish? I also want to install a filter in the future? How do i start with an old water and fish in my tank? I’m a first time fish owner. 🙂 thanks!

    • Hey Nikki! Thanks for stopping by. =] First, I want to applaud you for upgrading Chowder (nice name lol) to a 5gal tank. Honestly, pet stores shouldn’t even be selling 1 gallon fish tanks. They’re not really suitable for anything, with exception to snails/shrimp. Feel free to continue upgrading Chowder to bigger tanks, because you’ll definitely see that he will utilize the entire tank.

      There’s a misconception out there about how to keep Bettas and it’s perpetuated through uninformed websites and pet stores. For instance, Bettas do not live in puddles in the wild. They live in large, but shallow bodies of water (rice paddy fields). I used to keep my little guy in a 10gal, before I upgraded him to a 20gal Long. 5gal is fine, but if you have the money/room to upgrade, I’d recommend it. You get a lot more out of a slightly larger tank.

      I’m curious, since you’re not using a filter… do you use live plants? There needs to be something in the tank that will cleanse the water of the waste created from food/fish bi-products. If you have live plants, you can probably bypass the filter, since many plants (especially stem/floating plants) will consume more waste than one Betta can create. Just be weary of how much food you feed, so that you’re not polluting Chowder’s environment. Otherwise, go get yourself a cheap sponge filter and an air pump. That’s probably the cheapest man-made filtration you can purchase and requires the least amount of maintenance. Plus, your Betta will appreciate the lack of current, rather than having to deal with a cascading waterfall from the likes of most other filtration devices.

      Nikki, adding more water will never shock your fish, unless it’s not dechlorinated or too warm/too cold. If you dechlorinate your water and it’s either slightly cooler or the same temp as the water in the tank, just add it all at once. There’s no need for this 20% addition. Cooler water will simulate rainfall, which I’ve found most fish typically enjoy. Watch his behavior once you do this. It’ll probably be a fun treat. =]

  13. Hi there,

    I have really enjoyed all your info on fish in cycling. Here is my problem. I have 3 Roseline Sharks in. 50gallon bow front tank. I started cycling the tank 5 weeks ago. I added the fish 2 weeks in. I am doing 50% water changes every day because my ammonia reading is showing 8ppm. My nitrites are 0 and the nitrates are .25. I have a marine land Emperor 400 filter along with a extra large sponge filter. The fish seem fine. They are eating like pigs and active. I can’t figure out why the reading is so high. I eventually want to add discus to this tank. But know the water peramiters need to be pretty much perfect before I consider even looking at buying them. Do you have any advise for me? I am using the API test kits to check my levels. Any helpful advise would be wonderful.

    • Hi Brandie,

      Thank you for your interest in the site. It’s certainly much appreciated and I apologize for getting back to you so late in the game. This site has kind of taken a backseat to life, recently, but I hope to get back at it again in the near future.

      It sounds to me like you might have ammonia in your tap, if you’re getting a reading that high. Either that or you have the wrong type of soil (or uncapped soil) in your planted tank (if it’s planted). 3 Roselines in a 50gal isn’t going to be able to produce that much ammonia. That said, your 50% changes aren’t going to do it, alone. Your filters can also cause spikes in ammonia or nitrates, so you should try giving that a good cleaning. By cleaning, I mean rinsing out all of your filter media in dechlorinated water (or old tank water). After you clean the filter, conduct a large water change. I’d take 75-80% of the water out. You might need to do that two or three times to rid the tank of ammonia, altogether. None of this will have an effect on the biological bacteria you’ve been growing in the tank, so you needn’t worry about that.

      I hope everything turns out well. Sorry, again, for getting back to you so late.


  14. Hi 🙂
    I’m in the middle (at least I think) of cycling my 8.5 gallon tank. I have 3 male guppies and they seem to be thriving.

    I have been testing water at least every other day and changing the water at least twice a week. I have yet to see any trace of Nitrates or Nitrites.
    I had a spike in Ammonia about 3/4 weeks ago and went to an aquarium store and the owner instructed me to feed way less as I was way overfeeding them, change water every two days and add Seachum Stability. I was to follow this process till the level dropped. Well the ammonia level did drop, however I CAN NOT seem to get the level of ammonia to get below .25!
    Is this normal and am I just in the “be patient” part of cycling? Or is there something more I should be doing?
    Also each time I do a water change, I replace about 25% of the water and I vacuum about 1/3 of the tank. Is it advisable to vacuum each time at this point? When I do vacuum I can see a lot of debris being sucked up even though I am feeding once every other day.
    I thank you in advance for your time! Hopfully I can get this under control without any casualties!

  15. Hi Kevin

    Have spent the evening reading your website, some really great advice and i hope you can help me out with a bit more !

    Basically i was fed some dodgy info by my local pet store and have ended up trying to cycle my tank with 3 Zebra Danios.

    I have a 64 Litre tank, Real Plants, 1 Airstone, Heater set to 24C and a interpet CF2 filter

    Only since setting up the aquarium have i read up on the nitrogen cycle and now am semi forced to go down the fish-in route.

    I have got the API master kit and have been testing the water for the last week or so, im not sure what the next step is. Here are my measurements

    PH – 7.6
    Ammonia – 0.25
    Nitrite – 2.0
    Nitrate – 20

    PH – 7.6
    Ammonia – 0250.50
    Nitrite – 2.0
    Nitrate – 40

    PH – 7.6
    Ammonia – 0.50
    Nitrite – 2.0
    Nitrate – 20

    I am feeding them once a day, just a few flakes (they look so hungry !)
    Basically so confused over water changes, whether to use a product like Tetra Safestart or just take the fish back to the store.

    Any advice would be more than welcome sir


    Paul and the kids

    • Hey Paul and the kids! Thanks for stopping by.

      Zebra Danios typically aren’t the biggest contributors to waste and ammonia production, so it’s surprising to see your results. When did you set this tank up? I imagine it was some time after purchasing your Danios, that you started testing parameters. It’s odd that you’re seeing Ammonia, Nitrites and Nitrates at the same time. Not unheard of, but still a bit odd. Have you tested your tap water, to see what your base line is? You might be adding ammonia from your tap into your tank, which will throw off your readings. Typically the ammonia found in tap is ammonium, so it’s harmless to the fish (but still utilized by plants). So, while it would be harmless, it’s still competing with the other waste elements in the tank, in terms of plant and bacteria food, plus possibly throwing off your readings.

      Have you been conducting water changes? You’ll want to conduct at least a 50% pwc to get all of your values down. You want to see 0 ammonia, 0 nitrites and only up to 10-20ppm Nitrates. Those are acceptable readings. It’s possible to get 0ppm Nitrates with plants, but if you don’t have heavy eating plants, then expect that 10-20 range. If one water change doesn’t do it, do another one. You can change 100% of the water, if need be. As long as you use dechlorinator, your biological bacteria will be fine. Once you get those readings down, test your parameters again and see where you’re sitting in another day.

      If you need additional assistance, please feel free to e-mail me, using the contact form.

      Hope that helps a bit,

  16. How wonderful of you to sacrifice your time and share your knowledge!
    I am bookmarking this page since i was forced to start my fish in cycle today…thanks to the petstore…i am reading up on all the info i can get and hope fish (Betta) and myself will come out of the fish in cycle ok…
    i have added lots of plants, floating ferns etc..
    Thanks again for sharing!

    • Thank you Britta, I really appreciate that! No problem at all. I’m glad you find this useful. =]

      Please let me know if I can be of any assistance.


  17. Due to a massive ich infestation, I am cycling a 44 gallon tank with 6 mature cichlids in it, they seem to be healthy, I’m testing my water, conditioning….. my only problem is that I have cloudy water caused by a bacteria bloom, it’s been cloudy for two weeks now, I have 2 filters and two bubblers so it’s not waste, it isn’t green so it isn’t algae, I’ve read up on it and a lot of sites are telling me to wait it out, any thoughts our advice


  18. Hi there!

    Thank you for an incredibly informative article – it’s nice and to the point, and doesn’t make one feel terribly guilty (as I do) about suddenly buying a fish thank for the first time, along with some fish.

    I’m wondering if you could advise me on what to do:

    I currently have a 65 litre (15 gallon) fish tank with three dwarf puffer fish in. The gentleman at my local fish store had said I just needed to put water in, along with a dechlorinator, and that it would be fine. He also gave me 7 dwarf puffers (a mistake) and said they would be fine, and that they just need lots of plants because they get territorial. And he sold me a NitrAte test kit because he said that was all I needed.

    After setting it up, 4 of my puffs died within two days. I was so, so heartbroken and guilty (still am) and did some research. Turns out that puffer fish have a massive bioload, and had probably passed on from ammonia poisoning.

    Jump forward one week – the remaining three are loving life and thriving. I’ve since been trying to get this cycle going. I obtained a used filter from the fish store a few days ago and have been running that in my tank along with my new filter. I bought an ammonia and nitrite liquid testing kit, and have been doing 50-70% water changes twice a day. My ammonia reading seems to be between 0 – 0.25 (it’s not as green as the 0.25). I haven’t had any nitrites yet, but have suddenly started getting a nitrate reading of about 12.5. This is weird since I would’ve expected nitrites first. I’ve been doing all the tests about three times a day, and the ammonia test about 6-7 times a day.

    I’m going now to the fish store to get some used gravel to help speed up the cycle.

    The current fish aren’t displaying any symptoms that the previous fish did. I just want to know – I am aware that it may take time to cycle the tank by just using old media and lots of water changes (I don’t want to use any quick start bacteria-in-a-bottle stuff. Will this be extremely harmful to my puffs? I’m keeping an eye on the ammonia readings at all times.

    I’d appreciate any help! I love these puffs to bits and I don’t want to lose them. I’ll do a million water changes a day if needs be. I just need to know that not all is lost and that the cycle will happen! And an explanation of why I would be getting nitrate readings with no nitrite readings.

    Thanks in advance! Keep up the awesome articles. 🙂

    Kind regards,


  19. So I have had my 10 gallon tank up and running for 2 weeks , started out using the Nat Geo New tank stuff out of curiosity , added beneficial bacteria, de chlorinator and pH balancer now my ammonia is normally between .30 and .15 and I have 9 fish , all mollies but two. In fact they have already had 3 babies one of which died but the other two fry are lively and have been for 4 days . and super small. I do a 50% water change ever other day with a dechlorinator and ammonia balancer. My filter media had swelled and i currently have water overflowing not much but some is bypassing the media . should I change it ? Orrr ?

  20. Please Help! My head just may explode from all this cycling info!! My grandson got a betta fish and he has been in a 1/2 gallon tank with no filter for about 1 month now. He has small amount substrate, one fake plant and a fish cave decor. We just got a 3.5 gallon tank for him with filter, heater and will be adding live plants (upgrade bigger down the road. Seeing that he is already in a non cycled tank, should I just put him in his new tank with his substrate, fake pant and decor (to transfer any bacteria it has) and go from there trying to cycle with him in it…wouldn’t that be better then leaving him unfiltered no cycle tank he is in now? I am going to try hard to get someone’s filter media if I can locate someone. Or should I leave him where he is and do new tank separate? Should I use Dr. Tim One & Only or Tetra Safe Start and also possibly borrowed media if I can get some? Will one betta produce enough ammonia to feed the safestart or the bacteria from borrowed media filter (if I get) or will it die off due to not enough? Thank you for any help you can give, because my thoughts are now consumed with confusion of this darn cute fish!

  21. I NEED HELP!! My poor fiah! I’m in waaay over my head. I got a tank and fish before I knew enough. I went and baught a 10 gal tank. It has a whisper filtration system bubble wand. I have no Thermometer though. I think my mistake started from the very beginning…I filled the tank with water. Then put almost the whole small bottle of safe start into the water, then almost immediately added a teaspoon of aquasafe. Then I turned on everything and let the fish bags float on the water. I also go too many fish I think? ( 2 black Molly’s, 2 orange and black Molly’s, 4 Guppy’s, and 6 neon tetras) I did all this on thurs night. I’ve been feeding them twice a day until now! So now ive started reading up and got scared I had too much amonia…no test kit either..its now sat night and added the rest of the safestart.( about 7 or 8 ml??) Hoping the good bacteria will help with the bad? Idk!! Idk what to do! I don’t want my poor fishys sick or worse…and I don’t want my two and three year old to be upset either…it was their birthday present 🙁 please help me!!!

    • Well nuts! Kayla, I’m very sorry to hear about this and I’m very sorry to have read this so late. I ran into some issues with the website a few months back and finally found the time to fix it recently. I’m hoping to be a bit more active than I was in the past, but we’ll see.

      Since it’s been about 5 months, I expect you’ve either lost several fish and have a few lingers, lost the whole batch and gave up, or found help elsewhere. I hope you found help and I really hope you didn’t give up, yet! Of course I hope you were able to save as many fish as you could.

      Believe it or not, this is how it goes for a lot of new fish keepers. Fish tanks are often a spur of the moment purchase. You get some help at the store (very limited, usually), they up-sell you a ton of stuff that you really don’t need, you get home, set everything up and realize you don’t know what’s next, when it comes to caring for aquatic creatures. It’s almost second nature when it comes to other pets, because we’re land-dwellers, they’re land-dwellers… we all breathe the oxygen in the air. Pretty cut and dry stuff. lol Not so much for fish.

      First thing to note: You do not need safe start. It has never been proven to be of any help or use in a fish tank. A general rule of thumb is that chemicals are typically never ever needed when fish keeping. The only types of chemicals you might need are medicines and dechlorinator (like Tetra AquaSafe or Seachem Safe), but that’s about it. Everything else can be obtained naturally. I’m quite certain the pet store you bought the tank from probably up-sold you the safe start, and that’s only because it happened to me when I first got my start. =]

      The only tried and true method of growing bacteria in the tank is through cycling with fish or otherwise (flakes or shrimp, etc). Any additives that claim to do the same thing are more like snake oil.

      For a 10gal tank, 2 black mollys, 2 orange and black mollys, 4 guppys and 6 neons are definitely too many fish for that small tank. When you purchased the fish, they were babies, but rest assured they will grow (especially the mollys, which will likely get about 2-3″ in length). Not only that, but now you’re dealing with livebearers, and that’s just asking for trouble in such a small tank. They constantly procreate (the mollys and guppys), so your overstocked tank will become even more-so in due time. You could definitely get away with a small school of Neons w/ some guppys, but leave the mollys out of it. They’re going to grow too large for a 10gal tank.

      Another thing to note is your feeding schedule. Fish do not have to eat twice a day. Heck, they don’t even have to eat once every day. You can get away with every other day and your fish will be healthy as can be. It’s always more dangerous to overfeed fish, than it is to underfeed. Of course, starving is out of the question, but fish can go without eating for about a week or even more. I’ve gone on vacation without a house sitter for up to 6-7 days without issue. In fact, many times, my fish seem more healthy than I left them. That said… I do keep live plants in my tanks, and there’s usually some chomping going on over that extended period of time.

      Anyway, just keep an eye on your feedings. You don’t need to overdo it. =]

      So, the solution of your problem is just to relax. These things happen. I would suggest taking back the mollys. Unfortunately, Neons are not very hardy fish, but guppys are pretty decent. Zebra Danios are a good options as a replacement, though, and you could fish-in cycle with them. Otherwise, you could always take back every fish and start fresh with fishless cycling.

      I know that many people do tend to give up on fish keeping after these types of experiences, but that’s merely because things feel overwhelming after you’ve just jumped in. If you did give up, I would say give it another shot. I would also go with a 20gal long tank, instead of a 10gal. The step up really gives you a lot more room and choices to work with, but still doesn’t take up that much real estate.

      I hope you got things sorted, but if not, please feel free to e-mail me at kevin at

      Thanks for stopping by and hope things are going well.


  22. hi
    im just about to cycle my new 50 gal tank im using real plants just wondering whats the best hardy fish in a big tank and how many would recommend for a tropical tank and good advice in your post really helped me out thanks mate

    • This is quite a bit late, but the best advice here (if you don’t have fish, yet), is not to use fish. Fish-In cycling can be quite a bit more demanding on the fish keeper, because you’re not only trying to build bacteria, but you’re trying to keep the fish alive. My advice would be to use Ammonia for Fishless Cycling. That said, I understand that it can be very difficult to find Ammonia in some countries. If that’s the case, you could certainly use a raw shrimp or fish flakes in its stead. Same process, really, but Ammonia is much faster.

      If you’re settled on fish, however, my suggestion would be to go with a small school of Danios. Giant Danios would probably be good for the 50gal, but I would stick with about 4, since they get larger. Otherwise, you could get a school of Zebra Danios or the like. Some people suggest some species of Corydoras, but I think that’s risky. Corys are very hardy, yes, but they’re bottom dwellers. The most dangerous place in a tank, when you’re cycling, is the bottom of the water column. That’s because the waste builds up there, and Ammonia/Nitrites/Nitrates can be found in its highest concentration. This is one of the reasons filter intakes are along the bottom of tanks. So, it’s best to keep away from any bottom dwellers when cycling a tank.

      Thanks for stopping by!


  23. Hi you mentioned doing water changes when the ammonia or nitrites are higher than 0.25ppm, what percent of the water should be changed? 50%?

    • Unfortunately, there’s no set amount to remove ammonia or nitrites. Since the bacteria you’re building is in the filter (and covering other objects, like plants, ornaments, gravel/rocks, etc. you can change as much as 100% of the water if you’d like, without any negative effects to the bacteria. I would try 50% and see what that gets you. If you’re still reading above .25ppm, you should conduct another one. I’ve run into instances where it takes multiple water changes to bring the readings down. It can get frustrating, but don’t become distraught. It’s all very normal and just part of the process.

      Thanks for stopping by and good luck!


  24. Hi I’m two weeks into a fish in cycle on a 60g and so far my ammonia hasn’t gone above .25. Its stocked with 6 haps/peacocks that I’ve been feeding every 1 1/2 days. I’ve been using seachem stability and prime daily for the past four days and doing 10 percent water changes every other day. All other reading are at zero and ph is at 8.4. I’m using the api master test kit. Just trying to figure out if I’m on the right path or should I be doing something else because my cycle seems to be stuck in the ammonia stage.

    • Hey Jeffery,

      Keep in mind that all cycles are different, in terms of how long they’ll take. That said, have you tested for nitrites yet? The test might not show anything, because the nitrite levels are so low, but it’s possible that it’s already begun to develop. You might want to test out your cycle, by changing water until you have a starting point of 0ppm Ammonia, to see how long it takes for Ammonia to reach .25ppm again. If it takes longer than previously, then you’re surely on your way. If you can be patient, just stay the course, but it’s unlikely that your cycle has stalled. The bacteria will grow, given the water parameters are appropriate. Keep in mind that your pH is a little high and that can cause Nitrosomonas marina to develop more slowly than within the optimum levels of 6-7 and even up to 8ph. Now, pH can certainly rise with waste and Ammonia present in the tank (decaying material typically softens the water), so if you do decide to change your water until you have 0ppm Ammonia, take your pH measurements again to see what’s “normal” in your tank.

      You should always know your starting points, just in case anything changes (and they usually will).

      • I tested today and ammonia dropped down to zero. Nitrite and nitrate are also reading zero. The reason for the high ph is because the water in my area is high. I have tested the tap water and its actually higher. I’ve also tested my 10g that’s a year old and it’s also at 8.4. Pretty much everything in my tank has consistently read the same since day one except for the ammonia.

        • Ok, this could mean one of three things: Your cycle crashed, your cycle is finished, or your nitrites/nitrates are still so low that they’re not readable by your test kit, but your Nitrosomonas marina colonies are ready and established. Do you also have plants in your tank? If so, that could give false readings of ammonia, as well, since ammonia is a natural fertilizer.

          That’s fine about the pH. If it’s normal, it’s normal. The disasters come, when you start using chemicals to alter your pH.

          • I found out my problem. I was not shaking up nitrate bottle number 2 and was getting a false reading. My reading now are:

            Ph 8.2
            Total Amm: .25
            Free Amm 0.02
            Nitrite: 0
            Nitrate: 10

  25. I just set up a 36 gal aquarium. It has been years since I had one.
    Here is what I did. Rinsed everything off and staged the decorations. Filled it with mineral water (looking back I should have gotten distilled) put in two bags of bacteria and also the right amount of the water de-chlorination stuff. In 24 hours I tested the water and all the levels are right where they should be except the Alkaline levels.
    I am thinking the alkaline levels are high because I used mineral water instead of distilled, does that make sense?
    I left the water level 4 inches from the top in case I need to adjust it. I was thinking of adding a half gallon of distilled tonight and checking it tomorrow and just keep adding till it gets to acceptable levels over the next few days.
    I stocked it with one of each of these to help speed up the eco process. Not surprisingly the neon died but the other fish seem really active. I thought you’d like this Board on Pinterest…
    Let me know your thoughts… I am aware that I will probably have a few more casualties 😞

    • Hey Ike!

      Thanks for stopping by. To start, I think you’re right. Adding mineral water probably had an effect on your alkaline levels. My question, however, is to ask why you thought you needed to use mineral or distilled water in the first place? How is the water out of your tap? Do you have very hard water?

      That said, I have no idea what the TDS reading would be in mineral water, so it’s possible that mineral water would have little effect on pH. What is the pH out of your tap? I assume you took the readings, which is how you know they’re off.

      Also, did you add the bacteria to the water before adding the dechlorinator or after? If it was before, you can bet that the bacteria is mostly dead. After and you should be ok. I’m not a true believer in the bagged/bottled pre-built bacteria colonies, myself… I don’t think they’ve been proven to work, since you still need to cycle a tank after adding it.

      You said that your readings are on point, but what’s on point? Can you give me your readings of whatever it is you tested for?

      Why did you leave 4″ at the top of the tank? Not sure I understand what you’re trying to accomplish there. More water in the water column is arguably better in a tank, since it gives you more room for error, allows for more stocking, and dissipates waste a little better, allowing your plants/bacteria colonies to work effectively and efficiently.

      Well, Neons are rather delicate in the best case scenerios, so it’s not surprising that he’s the first to pass. However, if you only purchased one of each, stress could have been a factor. It’s hard to know, not knowing the parameters in the tank, but the other, bigger (except the guppies) fish could have tormented the Neon to death, or seeing the larger fish and being without a school, he could have stressed himself out until succumbing to death.

      The others are ok on their own, but neons should always be kept in a school. There are arguments over what an appropriate school should be, but as long as you have 4 or more, you should be fine. That said, neons aren’t the best fish to cycle a tank with. If you want something more hardy, go for some Zebra Danios. Very hardy and just as small. Not as flashy, but still pretty.

      Mollys add to the bioload quite a bit. In that, I mean they create a lot of waste, because they’re very active, eat a lot, poop a lot, and of course… breed a lot. You have two in the tank, which means they could mate, but just be aware that they do contribute to the bioload in a big way. Very hardy, though, just as Gouramis are.

      The only problem I have with Dwarf Gouramis, is that they’re not very hardy… especially in comparison to their non-dwarf cousins. This isn’t the fault of the gouramis, of course… it’s the fault of over-breeding and inbreeding. They’ve become so popular and so mass produced that they’ve developed a disease all their own: Dwarf Gourami Disease (or Dwarf Gourami Iridovirus). Not every Dwarf Gourami gets it, but just be aware that although most Gouramis are hardy and can usually live throughout a fish-in cycle, Dwarves are susceptible to this disease. It’s not easily treatable and you’ll know when it death spirals. I’ve unfortunately had to deal with this in the past and it’s very sad to see and witness, knowing you can’t treat or do anything about it. Just wanted to put that out there, so you know it when/if you see it. It’s not necessarily due to the contaminants in your tank.

      Since you have a 36gal tank, you could invest in a Blue or Opaline Gourami. They’re quite beautiful, very hardy, and always out and about. Love mine. I have her in a 75gal tank, but a 36gal should be room enough.

      Anyway, if you’re still around, let me know what’s going on and how you decide to proceed. I’d love to follow along. =]

  26. Hello, I’d love some help on this big issue I’m having .

    I’m new to fish care. I had a goldfish a long time ago and never had anything else until now.
    I now have a 5 gallon I got one week ago. 

    So I’ll start with what I have going on in my tank.
    My tank is a Marineland Nook 5 stocked with 5 guppies, 1 male betta and two otocinclus for cleaning.
    My Tank has a gravel bottom with plenty of plants and tablets to help their growth. A heater and a decent filter. Before I added the fish in I treated the water and all has been great.
    It’s been a week today. When I woke up this morning, my little betta boy was floating in the corner gasping for air. He has white furry puffs covering his head and fins, red blotches, his normally shiny blue scales were gray and dull. He was perfectly fine in the morning.
    I rushed to the store and got a bottle of Pima fix and Betta fix and separated him from the rest of the fish in a different bowl with the same water. I brought a sample of water to trest and found I had high ammonia levels. So upon getting home I did a complete water change and cleaned everything.
    Unfortunately my Betta, Bicus did not make it and died shorty after being treated.

    I put my guppies and suckers in the now less populated tank and at first it seemed fine but my guppies started hovering at the top of the tank, like my betta did. 
    Just in case I treated my tank with Pima fix and they seem better but their not swimming along the tank like they used to.

    Would it be possible to give me any advice? Or maybe on what I did wrong to cause my bettas death?
    I was told to cycle my tank, how do I go about this with fish?

  27. Hi, thank you for providing all this information.

    I am a beginner with starting a tank and have 2 small comet goldfish in a 12 litre tank. My tank is about 3 weeks old and hasn’t cycled. My ammonia and nitrate levels are 2.0ppm which after reading these posts I see is dangerously high. I have been doing 10% water changes
    every 2 or 3 days for the past 3 weeks and been using water conditioner. I also put in sera bio nitirivec when I do these water changes as advised by the pet shop. But now am getting concerned as my ammonia and nitrate levels are not dropping. I went to the pet shop yesterday and they advised I stop doing the water changes so frequently as this will start to stress the fish and that I only use sera bio nitirivec in larger quantities more often. I put in 10 ml sera bio nitrivec yesterday. Please help I’m not sure what is the right advise or what more can I do. Thanks.

  28. Hi, I have gained a lot of knowledge from you info. Thanks for your time it is greatly appreciated. My question is, I have one betta i brought home from work which no one was taking care of. This little guy has been in a 1 gallon for quite some time. I went out and got him a 20 gal long with heater and filter. I also got 2 plants in there with a nice fake wood stump with places for him to hide. He is now still in the 1 gal which im on top of with water parameters. My question is can i safely cycle the the 20gal with the fish in? I just want him to be safe and happy.

    • Hi Robert,

      I’m very sorry for the delay in getting back to you. It’s been a crazy few months (just moved into a new home and had a wonderful debacle with Verizon – so I was without internet for a couple of weeks)!

      I’m so glad you find the site useful and truly appreciate your thanks! Also, I commend you for taking on the responsibility for the lonely Betta! They’re wonderful, inquisitive creatures with a lot of character… yet, often misunderstood and rarely taken good care of. It sounds like you’re on your way to making a great home for your new friend, though. He’ll definitely appreciate that 20gal much more than the 1gal. I kept mine in a 20gal long and he made full use of the tank. Loved that fish – so fun to watch and interact with. They’re a lot smarter than you’d think.

      I’m probably to late to the party, but hey, you never know who’s reading. Plants and other decor for a betta are great. They’ll use plant leaves for support, as they rest, for shade/shelter, and the plants will pull double duty by also cleansing the water column.

      Most would suggest that there’s really no way to “safely” cycle a tank with the fish you want to keep. Ammonia can cause a lot of havoc with your fish’s immune system and will likely shorten its life. However, you have two things working in your favor.

      First, you have a Betta. Bettas are anabantoids aka labyrinth fish, so-called because they have a labyrinth organ which acts as a lung. This organ allows the Betta to breathe air from the surface of the water. Why is this helpful? It allows Bettas to live in water that is typically more toxic/dirty than other fish are capable of living in. Fish that must breathe through gills, will intake toxic water, so not only are they swimming in it, they’re also breathing it. This is more harmful and will likely burn their gills (ammonia burn).

      Second, you have live plants. Plants will offset the waste that your fish will produce. With a 20gal tank and only having one fish, you’ll likely never see a spike in ammonia, nitrites or nitrates. The Betta is so lax, his food intake is minimal and he won’t be producing as much waste as a more active fish. Even with the waste this fish will produce, the plants will likely eliminate 90-99% of it, utilizing the fertilizer to grow (aquatic plants actually use ammonia, nitrites and nitrates – some more than others).

      Anyway, long story short, you should be safe with adding the Betta to your 20gal tank. Just keep an eye on things every now and again and don’t over feed.

      Thanks for stopping by and hope you have/had an easy transition!


  29. Hi, I just got a new 10g tank and currently doing an Fish-In-Cycle with 2 tetras. I got my water checked at Petco, and they said everything was doing fine. I acclimated my fishies to the new tank and I thought everything was going smoothly. I don’t know much about fish, this is my first tank, so I was wondering if having my fish swim at the surface of the tank being normal? I don’t think they’re gasping for air, but I’m worried that I might be killing them oh so slowly. Furthermore, there seems to be a clear film at the the surface. Is that normal or should I be concerned?

    • Hi Mary-Grace! Thanks for stopping by and congrats on the new tank!

      I’m curious if you added anything to the tank, that you might get from Petco, to treat your water? Some additives will create an oil-like slick on the surface of the water column. Algae, bacteria, decay could all be culprits, but it’s hard to tell from just a short description.

      Only having two tetras (which kind?) would lead me to believe that you probably don’t have a bacteria problem. The poop the fish will produce will be minimal enough not to push the envelope there. The only cause for decay would be for food, poop and live plant matter. I’m assuming that you don’t have live plants and we’ve already addressed the pooping issue. My main concern would be that you may be feeding your fish too much.

      How much and how often do you feed them? I’m curious about your filtration, as well. I typically would recommend increasing your filtration by a factor of 2, so if you have a 10gal tank, you should be using a filter for a 20gal tank. In addition to this, you need to break up the surface tension with the filtration device. This will add oxygen to the water column in addition to eliminating the chance for algae to create an oil slick at the surface.

      That would address the oil slick problem. However, since you’re doing a fish-in cycle, you need to be prepared for ammonia buildup (caused by decay, as well). If you’re overfeeding your fish, they will not eat all of it. They’ll only eat a small portion at any given time. Also, the more they eat, the more they poop… so, that adds to decay. Fish also pee and shed their slime coat, as well. All of these things contribute to waste in the water column. My guess, as to why the fish are at the top of the water column, is that the lower areas of the tank are too toxic for them. I think you’ll probably find that the ammonia might be building up, and in the case of an aquarium, the bottom areas of the tank will always be the most toxic, as waste increases.

      Do you have an ammonia/nitrite/nitrate test kit? If you don’t, I would recommend purchasing a Master Test Kit (

      Please feel free to post your answers and/or additional questions below. Hopefully we can get to the bottom of what’s happening, before anything bad happens to your two new little fishes. =]

      Thanks again,

  30. Hello and thank you for the information!
    I currently have a 20g tank with one common goldfish. Suddenly his water has become very cloudy no matter what I do but the parameters read well consistently. This morning it was PH @ 7.5, nitrite @ 0, Nitrate @ 0, ammonia @ just over 0 (it wasn’t bright yellow, it did have a slight green to it but was nowhere near the 0.25 mark) and the phosphates are nearing 0.25 which Im positive I can control with my Phosguard pack.
    That being said, how do I clear up the constant cloudiness? I’ve just ordered a AquaClear 30 to replace my (I assume) under-preforming Whisper 20 – I plan to put the old filter media in the new filter to establish a good bio cycle and will begin 50% water changes every other day. Im also going to reduce feedings to once every other day. Does this seem sufficient? What are my goals parameter-wise when replacing so much water?
    Thank you for your help!

    • Hi Jesika!

      Hope I’m not too late and you’re still doing ok with your goldfish. It seems like you’re on the right track and you’re taking the necessary steps to create a great living environment for your new friend.

      There could be one of two things happening in your tank, with the cloudiness: 1. it could be an algae bloom, or 2. it could be a bacterial bloom. Either one is normal, especially in the beginning stages of cycling your tank.

      When you have high phosphates or ammonia/nitrates/nitrites (and especially not a lot of plants), this creates a suitable environment for algae growth. Algae, like plants, thrive on ammonia and nitrates, especially, and if you haven’t established an equilibrium in the tank, yet (with biological bacteria, bottom feeders, etc), mineralization of decaying/dead matter will result in the by-product of phosphates. Phosphates are another reactive nutrient that algae (and plants) love. If you have no plants, you’re just going to feed the growing algae. This is my guess as to what your cloudiness is – an algae bloom (sudden, expedient growth of algae).

      If it wasn’t an algae bloom, it could be a bacterial bloom. This is when you have a sudden growth of biological bacteria, from your constant feeding of ammonia, resulting in the nitrogen cycle. It’s rare, but it happens in many cases. I, personally, have never had to deal with this (and I’ve cycled about 10 different tanks), but I do know others that have. It can be harmful to your fish, because it will spike the creation of one bacteria or another in the cycle, which could result in an influx of Nitrites or Nitrates. The way to handle this is to step up your water changes, however, it seems as though you’re doing a fine job of 50% changes. I wouldn’t worry too much about that.

      Hope that helps (even though I was late to the party)!


  31. please help all you expert fish keepers… im new to this hobby and i set up a 45 gallon freshwater tank in mid June and i did not cycle the tank before i added my fish… we’re now in July and I’ve been doing frequent water changes because my ammonia and nitrite levels are high…. my nitrite is like at 3 and ammonia i think is in the harmful range….. so Thursday i decided to get a bottle of dr tims one and only live nitrifying bacteria and i added the whole bottle Thursday evening….. i checked the water the next day and everything was the same and made me very frustrated so i decided to add a little prime seachem to detoxify the ammonia and nitrite…. maybe that was a mistake…i hope my bacteria didn’t die… so its now Saturday and my levels are STILL THE SAME!! i am so frustrated after spending so much to keep my fish happy and it doesnt seem to be doing anything…. so now im only left with doing water changes and feeding sparingly once every other day as recommended by fish store owners….. my fish totally seem happy..very active and always hungry so …im just confused and frustrated…i want the best for my fish … oh and i have all cichlids… one oscar.. 2 africans… 1 Jack dempsey and a convinct and firemouth… can someone PLEASE HELP ….. I’ve done everything i can think of…

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