What is the Nitrogen Cycle?

The Nitrogen Cycle is a fairly basic concept that everyone who maintains an aquarium should understand. It is the biological process that converts toxic substances (ammonia) in our aquariums to something (nitrates) that is less harmful to the inhabitants. This process involves the establishment of beneficial bacterial which break down fish and other wastes into less harmful compounds.

There are three stages of the nitrogen cycle as shown in this image.

In the first stage ammonia is formed from the fish and other waste in our aquariums. Ammonia is extremely toxic and needs to be converted to a less toxic compound.

In the second stage, nitrite forming bacteria (nitrosomonas) develop and convert this toxic ammonia to nitrite. Nitrite is less toxic but still extremely harmful to our aquarium inhabitants.

As nitrite becomes available a second form of bacteria develops (nitrospira) during the third and final stage of the Nitrogen Cycle. This bacteria converts the nitrite to an even less toxic compound, Nitrate.

The Nitrate that is produced is either removed during water changes or accumulates and is used as a fuel source for plants and/or algae in our aquariums.