Cycling Without Fish

For many years, the common method of cycling a tank has been to set everything up, then add a few hardy or "disposable" (a term that I personally find somewhat offensive) fish, then wait 4-6 weeks until the bacterial colonies which convert ammonia into nitrites into nitrates have become established. It is very common at this point for the stress caused by toxic ammonia and / or nitrites to kill some or in extreme cases all of your starter fish, no matter how hardy they're supposed to be. In addition, it's a well-known fact that the damage caused by high ammonia levels to the gills of a fish is, to some extent at least, permanent. Once the tank has been fully cycled, you can start adding fish slowly, usually at a rate of a couple every week or two, until capacity is reached. This slow addition allows time for the relatively small bacteria culture on your filter to grow until it can handle the increased bio-load. If done incorrectly, for example by adding too many fish at once after the cycle, an ammonia/nitrites spike can occur before the bacterial colony can adjust.

What is the effect of the fish added during cycling? Quite simply, through their digestive tracts and the food that we feed them, they are a source of ammonia, which the beneficial bacteria require to live and to multiply. While the above method is the traditional way of cycling a tank, it is neither the only nor the best way.

In order to properly cycle a tank, all that's required is the filter media, water movement (to supply oxygen to the bacterial colonies, an introduction of the right type of bacteria, and a source of ammonia. The best and most efficient source of ammonia is (surprisingly) pure ammonia. The household cleaning variety is perfect for this use, but make sure that it does not contain any additives or perfumes before using!

In order to cycle a tank using ammonia, start everything up and add some gravel from an established tank or a few potted plants (their roots contain all of the necessary bacteria, and the plants themselves do not seem to be harmed by this process). Then simply add 4-5 drops of ammonia per 10 gallons per day until you get a nitrite spike. Once you have nitrites, cut the ammonia back to 2-3 drops per 10 gallons per day until the nitrites disappear. When you get a 0 ppm nitrites reading, you have a fully cycled tank.

The advantages to this method are several. First and most importantly, in my reckoning, is that no fish are harmed during the cycling process. This means that you don't have to risk the fish you really want in the tank to a nasty death, or alternatively, find a new home for several fish that you were using to cycle the tank and no longer want. Secondly, no matter how cheap the fish, I can guarantee that 10 or 20 mL of ammonia is cheaper!

Thirdly, and this is of particular interest, the tank will cycle much faster by this method. I have used this method twice, the first time was on a 45 G tank with a fluidized bed filter, the second was on a 10 G tank with a lowly sponge filter. The time for complete cycling of these tanks was 12 days and 14 days respectively. Compare that with the standard method which averages 4-6 weeks.
Finally, once the tank has been cycled, the bacterial colony created by this method can handle a large bioload immediately. The amount of ammonia added to the tank during the cycle is significantly higher than what would be contributed by a small number of hardy fish, therefore, a much larger, healthier bacterial colony exists at the end of the cycle using ammonia than would if you used fish.

After cycling my 45 G, I immediately added 6 bosemani rainbowfish, 3 clown loaches and a plecostamus. This is far above the recommended stocking levels at the same stage if I had cycled with fish. All of the fish are very healthy, and there was no ammonia or nitrites spike after the addition of the fish.

The benefits of this method are obvious, and as far as I can tell, there are no disadvantages. Overdosing isn't a problem since there are no fish in the tank. Stop needlessly stressing / killing your fish. The next time you have a tank that you need to cycle, try this out. I guarantee you'll be pleased with the results.

When I wrote the article on fishless cycling in January 1999

(, I had no idea that it would gain popularity on the internet so quickly. What started as a very obscure idea has become a viable alternative for many newcomers and more experienced hobbyists alike, thanks mostly to promotional support from a few individuals who tried the idea out and then recommended it to others.

When I first wrote the article, I had tried this method out on two of my own tanks; since writing it, I've received feedback from literally dozens of individuals, and I now have a much better understanding of the process itself, and some potential pitfalls.


The advantages of this process over the traditional method of cycling a tank using a few small, hardy fish to get the bacterial colonies up and running all result from "front-end loading" the tank. The amount of ammonia added is far above that generated by a reasonable number of cycling fish, resulting in faster growth of the bacterial colonies, and larger colonies when you're finished. In practical terms, this means that your tank cycles faster (reports of anywhere from 10 days to 3 weeks, depending on the fish tank... compared to average of 4-6 weeks for traditionally cycled tanks), and that you can fully stock a tank when the cycle is complete. This latter point is of particular interest to keepers of african cichlids or other aggressive fish. If these fish are all added together as juveniles, they're much more tolerant of each other than if they're added in small groups after the first fish have established their territories. Of course, another big advantage is that no fish are subjected to high ammonia or nitrite concentrations, eliminating mortalities and ammonia/nitrite related illnesses which frequently occur in new tanks.

Alternative Recipe:

While the original recipe works quite well (4-5 drops NH3 / 10 gal / day until nitrite peaks, then reduce to 2-3 drops / 10 gal / day), it does NOT take into account varying concentrations of ammonia that are available. ACS grade ammonia, which I was using, is ~28% NH3, while most household cleaner grades vary from 4-10%, a fairly wide variation in concentration. Bottles that have been left open for long periods of time will be lower in concentration, as the NH3 gas escapes back into the atmosphere. With that in mind, I'd like to propose a different recipe, which was suggested by D_Man and others (thanks!): Add ammonia to the tank initially to obtain a reading on your ammonia kit of ~5 ppm. Record the amount of ammonia that this took. Then add that amount daily until the nitrite spikes. Once the nitrite is visible, cut back the daily dose of ammonia to ½ the original volume. One advantage of this method is that the ammonia spike occurs immediately... when adding 4-5 drops/10 gal/day, it could take 4-5 days before the ammonia reaches the same levels. This should result in an acceleration of the entire process, though by how much (on average) remains to be seen.

Sources of Bacteria:

While it is probable that the bacteria required for the conversion of ammonia and nitrite to nitrate exist at very low levels in most uncycled tanks, it greatly accelerates the process to inoculate the tank with a large dose of healthy bacteria to get things started. Good sources of beneficial bacteria are ranked from best to least:

1) Filter material (floss, sponge, biowheel, etc.) from an established, disease free tank.
2) Live Plants (preferrably potted, leave the rockwool on until cycling is finished). Crypts or amazon swords are good choices, and not too demanding.
3) Gravel from an established, disease free tank. (Many lfs will give this away if asked nicely)
4) Other ornaments (driftwood, rocks, etc.) from an established tank.
5) Squeezings from a filter sponge (any lfs should be willing to do this...)

There are also a number of commercial bacterial supplements (Cycle, Stress-Zyme, etc.) available. IMHO, without getting on a soapbox, these have very little to no effect, and are best left on the shelf. If you want to try it, go ahead, but I believe that any of the above options will be more effective, and most if not all of them will be cheaper.

Sources of Ammonia:

The most difficult part of the fishless cycling procedure, according to many postings on the message boards, involves finding a good source of ammonia. Ammonia used should be free of surfactants, perfumes, and colourants. Unfortunately, not everyone has access to ACS grade ammonium hydroxide. Always read the ingredients on the bottle. The best sources for Pure or Clear Ammonia are discount grocery stores or hardware stores. Often, the no-name brand is the stuff you're looking for. Some other people have reported success with the following brand names of ammonia: Top Crest or Whirl Clear Ammonia. To paraphrase RTR: If it doesn't list the ingredients, or say Clear Ammonia (or Pure Ammonia or 100% Ammonia, or Pure Ammonium Hydroxide), then leave it on the shelf and look elsewhere. Shake the bottle if you're not sure about it... ammonia with surfactants will foam, while good ammonia will not.

Water Changes and Ammonia Removing Chemicals:

A large water change (50-70%) should be done before adding any fish to the tank to lower nitrate levels, which can be a pain to bring down later. When changing the water during a fishless cycle, do NOT use dechlorinators that also sequester ammonia, such as the very popular Amquel. I have heard from at least one individual who did everything right with regards to cycling her tank using this method... the tank cycled quickly, then she did a water change, then added a reasonable fishload the following day with more than adequate filtration, and observed both an ammonia and a nitrite spike. The only explanation that I could think of after questioning her extensively led back to the Amquel. In a normal, established fish tank, the ammonia is being generated nearly constantly... in a fishless cycle however, the ammonia is added as a daily dose... IMO, it's concievable (though not really provable unless a lot more people experienced identical problems) that the Amquel temporarily deprived the bacteria of its food source, causing a minor die-back in the colony at the worst possible time... right before adding her fish. To be on the safe side, use a simple chlorine/chloriamine remover which does not affect your ammonia levels.

By similar logic, any other ammonia removing chemicals (eg. Ammo-lock) or resins (Amrid) should also be avoided while cycling... they will affect the cycle, extending it's duration or otherwise adversely affecting the bacterial colonies.

Too Much Ammonia?:

It IS possible to add too much ammonia to the tank (generally several times the amounts suggested in either recipe), as some individuals discovered by mistake (thanks Boozap). What happens in this case is that the ammonia will spike very far off the chart then the nitrite will spike as well (also way off the chart), and it will continue to spike for a very long time. Why? There are a couple of possibilities... the first is that the filter media and surfaces in the tank or oxygen levels are simply insufficient to grow and maintain a bacterial colony massive enough to convert all of the ammonia and all of the nitrite to nitrates. Another likely possibility is that the ammonia levels are high enough to inhibit growth (through a biofeedback mechanism) of the bacteria rather than promoting it. The solution is quite simple, however. If you realize that you've added way too much ammonia simply do a water change, or if necessary a series of water changes to bring the ammonia and/or nitrite levels back into the readable range on your test kit. Then proceed as normal with daily additions of ammonia until the tank is cycled.

Other Uses:

Fishless cycling is also very applicable to hospital/quarantine or fry growout tanks... when not in use, a maintenance dose of ammonia (eg. 2-3 drops/10 gallons) can be added daily to keep the tank cycled and ready for new fish indefinitely. Simply stop the addition the day before you want to buy your fish, take ammonia and nitrite tests to be certain that the levels are still zero, and do a water change to reduce nitrates.

Future of Fishless Cycling:

The future of this method is up to those of you out there that have tried this and like the method. If you do, please continue to promote it, whether on the internet, at your lfs, or at fish club meetings. Feel free to print off this or the original article for education purposes; the more people that know about this method the better. I'd be very happy if lfs caught on to this idea as have fishkeepers on the internet, and recommended it to newbies as a safer, cheaper way to do things. IMO, the number of people that didn't get frustrated in the early stages and thus continued with fishkeeping would make it worth their while. Please continue to give me feedback on the method, or to ask any questions you may have about it.