The Nitrogen Cycle and Biological Filtration in Aquariums

Ammonia is a substance which is produced in the aquarium from fish waste and uneaten food.  This is a compound which is extremely toxic to fish.

This compound is broken down into Nitrite by a bacteria called nitrosomonas.  Nitrite is also harmful to fish.  Another bacteria called Nitrobacter breaks down the Nitrite into Nitrate.

These colonies of bacteria are referred to as the Biological Filters of the Aquarium.

This is called the Nitrogen Cycle. The different compounds in the cycle are Ammonia-Nitrite-Nitrate.

In a new Aquarium which has just been set up, the beneficial bacteria which break down these compounds are absent.  Hence, Ammonia can accumulate and reach dangerous levels which can be harmful to fish.  Hence, fish should be added gradually over a period of weeks.  This gives time for the bacteria to develop and colonize the aquarium.

These useful bacteria take a long time to establish themselves.  They mostly live on the aquarium gravel and the filters.  You must be careful not to damage these bacteria.

Bacteria can be damaged by the use of medication such as potassium permanganate or by washing the aquarium gravel and the accessories using soap.

Nitrifying Bacteria and their role in an Aquarium

Nitrifying bacteria are bacteria which break down the ammonia released by the fish into nitrites and then nitrates. There are a very important part of the aquarium ecosystem.   Absence of nitrifying bacteria in the aquarium can lead to ammonia or nitrite poisoning and can kill fish.

There are two main species of bacteria which are a part of the nitrogen cycle. The nitrosomonas bacteria convert the ammonia into nitrite. The other species nitrobacter convert the nitrite into nitrates.

Hence, healthy and large colonies of both these beneficial bacteria are essential for the health of an aquarium.

When the aquarium is first started, it takes time for the bacteria to establish themselves. This can be accelerated by a process called cycling where water and gravel from and established aquarium is added to the new tank. This enables the quick growth of the bacteria.

The bacteria take time to grow and hence the tank should not be loaded with fish too quickly. Add a few fish in the beginning. Later when the bacteria colonies have established themselves, more fish can be added.

Once the bacteria have established themselves, it is necessary that they are not killed accidentally. Some fish medication will kill these bacteria. An example is potassium permanganate which is used to fight infections.

Aquarium tanks and filters should also never be washed with soap. Soap can kill these bacteria.