How to Cycle a Fish Tank

Tropical fresh water aquarium front view with lush foliage plants and some fishes yellow Pterophyllum Scalare and Cardinalis neon
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Every aquarium owner has to go through the tedious process of getting a new aquarium to cycle. Unfortunately, there is no way to instantly establish the necessary stable nitrogen cycle in a new aquarium. However, there are ways to shorten and jump-start the process while still relieving stress on the fish.

Fishless Cycling

The benefit of this method is that no fish are required to be in the tank; therefore, no fish are at risk of being lost. As long as you are willing to spend the time to follow the steps, fishless cycling can be achieved.

Fishless cycling accomplishes the same thing as starting a tank with fish in it. The difference is that ammonia is added to the tank to replicate the waste that would be produced by the fish. The key is testing and adding ammonia daily to keep the process going. Missing days means that your bacterial colonies will not continue to grow. In fact, they may die off.

Fishless cycling will not cycle the tank instantly. Just as the standard methods of establishing biological colonies in an aquarium take time, so does fishless cycling. However, it usually takes less time overall and is certainly easier on your fish.

Seeding the Biofilter

Seeding an aquarium is an age-old method for jump-starting the biological colonies in a new aquarium. A cup of gravel from a stable, established tank is placed in a bag and put into the filter. Another option is to take the foam insert or the ceramic rings from an established filter and place it in the new filter. With this method, transfer the seed media immediately or the bacteria will be shocked and then die off.

In all seed transfers, there are cautions to observe. Do not use seed material from an aquarium that has dramatically different water parameters than the new tank. The pH should be of a similar range. Also, never transfer seed bacteria from a tank with hard alkaline water to a tank with soft acidic water. Bacteria cannot withstand any water chemistry shock.

Make sure the source of your seed bacteria is a healthy tank. If there has been any disease recently in the tank, do not use colonized substrate from it, as you may be transferring unwanted pathogens.

Have the new tank set up and ready to go, ensuring that the water temperature and chemistries are stable and in the desired range. Transport the gravel or media while submerged in water from the tank it came from so that it is never exposed to open air. Fish should be added to the tank very shortly thereafter, otherwise, the bacterial colonies will not have a continued source of ammonia to feed them.

Maturing a New Filter

Another method to speed up the nitrogen cycling process is to place the filter that is to be used in the new tank on an already established tank and let it run side by side with the existing filtration system. After a week or so, this matured filter can be moved (submerged) and used, bringing with it biological colonies that are already growing.

Add fish the same day to ensure the bacteria are fed. But care should be taken not to stock the tank too heavily at first. It is not possible to fully stock a new, unestablished system without side effects. And yet, this method will still reduce the amount of time needed for the overall nitrogen cycling process.

Regardless of the transfer method used, there is no magic bullet to immediately establishing robust biological colonies; time is needed. So even if you think the tank has fully cycled, never add a large number of fish all at once.