The Nitrogen Cycle in Aquaponics

What is the Nitrogen Cycle?

The Nitrogen Cycle is a natural process whereby each of the various types of nitrifying bacteria are born and carry out a specific role. Each of the bacterium consumes the previous one and then gives birth to the next bacteria. The three compounds involved in the nitrogen cycle are ammonia NH3, nitrite NO2, and nitrate NO3.

How long does the Nitrogen Cycle Take?

In general the Nitrogen Cycle takes 30 days to complete, however there is no specific time frame as each pond or aquaponics setup is different. It varies depending on the number of fish, the size of the tank and number of plants in an aquaponics growbed.

Stage 1

The first stage in the nitrogen cycle is the production of ammonia. Ammonia comes from a few different sources - fish waste, decaying plant matter and decaying fish food. By adding fish to an aquaponics tank, ammonia is produced and so the nitrogen cycle begins.

Stage 2

The second stage of the nitrogen cycle begins around day 10. Nutrifying bacteria that convert ammonia to nitrite, called nitrosomonas, begin to appear and multiply. The nitrite reading if tested with a kit will peak around day 20.

Stage 3

The third stage of the Nitrogen Cycle is the conversion of nitrite into nitrate by the nitrobacter bacteria. The nitrobacter need oxygen and an ammonia source in order to grow and survive. Nitrate is the waste product that these bacteria produce and will start to peak around day 30.

How does the Nitrogen Cycle Relate to Aquaponics?

Plants take up nitrates as a fertiliser which they need to grow, thus removing excess nitrates from the water. This allows the process to begin over again and in a perfectly balanced system, keeps the water clean and the fish happy.

You can use a Freshwater Master Test Kit to check your levels of Ammonia, Nitrite and Nitrate in your aquaponics system.