Fishless Cycle / Nitrogen Cycle

The Basics (Nitrogen Cycle)

The "Nitrogen cycle" (more precisely, the Nitrification cycle) is the biological process that converts Ammonia into other, relatively harmless Nitrogen compounds. In nature, the volume of water per fish is extremely high, and waste products become diluted to low concentrations. In aquariums, however, it can take as little as a few hours for Ammonia concentrations to reach toxic levels.

When organisms give off wastes they excrete Nitrogen in some chemical form or another. For example, people rid themselves of it in the form of urea, while birds use uric acid. However, fishes and many other marine organisms give it off in the form Ammonia (NH3). Ammonia is also produced and released when the tissues of deceased organisms and fish foods decay due to bacterial action. The problem for the hobbyist is that this Ammonia is highly toxic and if it is allowed to build up in an aquarium the end result will be the death of the inhabitants 10 times out of 10.

The solution to this problem is a number of bacteria that "eat" Ammonia and use it for their own food source. Bacteria like Nitrosomonas, Nitrosococcus, and Nitrosospira will use the energy stored in the Ammonia molecule, then release the Nitrogen left over from the process as another form. In this case, it is combined with Oxygen and re-introduced to the environment as Nitrite (NO2).

Nitrite is also a deadly poison to tank inhabitants but there are other types of bacteria which will then use the Nitrite for food. These bacteria, Nitrobacter, Nitrococcus, and Nitrospira, add another Oxygen to the nitrite molecule and acquire energy in the process. The nitrite is thus converted to yet another Nitrogen-bearing compound called nitrate, which in reasonable quantities is non-toxic/"harmless" to tank inhabitants (NO3). We still need to control NO3 or one will experience problems with algae (e.g., Algae Bloom). Nitrate levels are controlled through periodic water changes which are usually ~15%-25% on a weekly basis.

The Basics (Fishless Cycle)

For many years, the common method of cycling a tank had been to set everything up, then add a few hardy or "disposable" fish, then wait 4-6 weeks until the bacterial colonies which convert Ammonia to Nitrites and then to 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. The second method - the purpose for my writing this - avoids the stress on the fish by artificially adding Ammonia, which we call "Fishless Cycle". 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. Another great advantage of fishless cycle is the flexibility of fully stocking a tank after the cycle is complete. This 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.

Pure Ammonia as initial element

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 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 it! Ammonia used should be free of surfactants, perfumes, and colorants. 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. 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 because Ammonia with surfactants will foam, while "good" Ammonia will not.

Other bacteria sources and ways to speed up the process

I strongly recommend the use of other sources that contain a sufficient amount of "good bacteria" in order to noticeably speed up the cycling process.

* Filter material (floss, sponge, cartridge, biowheel, etc.) from an established, disease-free tank.
* Gravel from an established, disease-free tank. (Very efficient source of bacteria. Possibility of getting it from friend or LFS)
* Other ornaments (driftwood, rocks, etc.) from an established tank.
* Squeezings from a filter sponge ("sponge mud" is very rich in bacteria)
* Live plants (if your tank is heavily planted, the chances are you won't see an Ammonia or nitrite spike if you track these parameters when cycling. In fact, the only indication that your tank has cycled may be the appearance of Nitrates. Even then you may not get a reading: heavily planted tanks with a light to moderate fish load often test zero Nitrates, since the plants take up some of the Ammonia before the bacteria convert it)
* Increase of temperature of the tank. Chemical reactions are accelerated at higher temperatures which will cause the bacteria to divide faster. Be careful not to raise it too much. Over a certain point, bacterial growth is impeded. I've found the mid- to high-eighties work well.
* Increase aeration.

References:
“Fishless Cycle” by Chris Cow Ph.D. Organic Chemistry
“Nitrogen Cycle” by TheKrib
“Biological Filtration Basics” by James Fatherree