Your Guide to Fishless Cycling

The bacteria employed in the process of fishless cycling thrive in a basic environment; they prefer a pH of around 8. Use chemical filters to achieve these conditions if they can't be met naturally.

This is necessary in a fish tank because fish expel ammonia as a metabolic byproduct, and, if concentrated, it can be extremely harmful to the fish themselves. In the wild, ammonia is adjusted in a number of ways, but none of them are present in artificial water tanks. Fishless cycling is necessary to replicate the healthy natural conditions.

The nitrogen cycle in aquariums is dependent on two genera of bacteria, Nitrosomonas and Nitrospira. Nitrosomonas bacteria are responsible for the conversion of ammonia (NH3) into nitrites, compounds with the ion NO2-, and Nitrospira carry out the conversion of nitrites into nitrates, compounds with the ion NO3-.

Nitrates are not as harmful to fish as ammonia. Furthermore, nitrates are necessary for the growth of plants. Simply including some aquatic plants in the aquarium will take care of that problem.

The process has to be done before you buy the fish, since, as explained before, fish produce ammonia, and the nitrogen-fixing bacteria need to be present in the tank before the fish are introduced.

►► Fishless cycling is done by adding some ammonia (ammonium hydroxide is ideal, since it is an aqueous solution of ammonia) to fresh tanks. This invites Nitrosomonas bacteria to get to work, turning it into nitrites.

►► If ammonia can't be added directly, add some fish food. This releases ammonia upon decay, but its amount can't be accurately measured.

►► Use an ammonia concentration test kit to achieve a 4-5 ppm (or 4-5 mg/L) concentration of ammonia. Keep checking the concentration of ammonia on a daily basis.

►► When the initial ammonia has been completely converted into nitrates (ammonia concentration falls to zero), it is a sign that the Nitrosomonas bacteria are healthy and thriving.

►► When ammonia levels drop, add some more ammonium hydroxide, and start testing for the concentration of nitrites. A fall in the nitrite level is an indicator of a healthy bacterial population of both Nitrosomonas and Nitrospira genera.

►► Introduce the fish when the nitrite levels fall to zero. If you keep the nitrite levels at zero without introducing more ammonia (artificially or naturally through fish), the bacterial populations will not be able to survive. One fishless cycle should take no more than 3-4 weeks.

When the tank has been prepared by fishless cycling, there is virtually no risk of new fish getting ill and dying from ammonia poisoning.