If you have been around the aquarium hobby for any length of time, you’ve probably heard about the aquarium cycle or nitrogen cycle. If you are just starting out in the hobby you need to know about it and how to control it.

The aquarium cycle is often cursed and is probably the leading cause of fish losses in our aquariums. Understanding cycling can mean the difference between success and the beginning of a long and satisfying hobby and a frustrating failure and another tank in a garage sale.

But what exactly is the Aquarium Cycle?

The aquarium or nitrogen cycle refers to the process of converting nitrogen containing compounds in our aquariums to less toxic forms. It starts with the waste products produced by our fish or with the decay of excess food or other materials in the aquarium. These products all contain ammonia.

Ammonia (NH3) is highly toxic to fish. In higher pH conditions, it can exist or be converted into a slightly less toxic form called ammonium (NH4). Ammonia or ammonium is converted by bacteria (NAME) in the aquarium to nitrite (NO2).

Nitrite is somewhat less toxic than either ammonia or ammonium but can still cause a large scale die-off if it is not eliminated. Nitrite is converted by (NAME) bacteria to nitrate (NO3). Nitrate is only toxic in extremely high concentrations.

Nitrate is usually removed from the aquarium by water changes although it can be converted to elemental nitrogen (N2) and oxygen (O2)in low oxygen conditions by anaerobic bacteria.
There is a secret weapon to short cut the nitrogen cycle. The nitrogen cycle can be assisted by adding live plants to the aquarium. Live plants use the various components of the nitrogen cycle as food and remove them from the water column.