Nitrogen cycle

In a nutshell: Fish excrete Ammonia, Ammonia gets converted by good bacteria into Nitrites. Nitrites get converted by other good bacteria into Nitrates. And plants absorb the Nitrates as nutrients to grow, completing the Nitrogen cycle. The water is returned to the fish tank where the cycle begins anew.

Understanding this aquaponics resources page is essential. Yet often overlooked because you cannot see it directly. You can visualise your aquaponics setup as a living organism. The water that is pumped around is like the bloodstream of this creature. The water contains removes waste products, transports it and transforms them into the nutrients that are needed in another location. Only to begin the cycle again, and again, and for an infinite more number of times.

There are five important steps in the Nitrogen Cycle process:
  1. Removing the waste products from the fish tank (Ammonia)
  2. Transforming the Ammonia into Nitrites
  3. Transforming the Nitrites into Nitrates
  4. Cleaning out the Nitrates from the water
  5. Returning the cleaned water to the fish tank
The first and last steps are performed by the pump. It is critical in the aquaponics system and it's continued operation must be ensured. Without the pump, elements of the aquaponics setup (such as the plants, the fish, or the bacteria) will start to die - just like organs starving off when the human heart stops working... just not as quickly after a failure.

The second and third steps of the Nitrogen Cycle are performed by bacteria. They are actually the workhorses of an aquaponics system. (Did you know, that there is actually more mass in bacteria in the system than fish? Hard to believe when you have a large system with hundreds of fish - just imagine how many bacteria live in the plant beds, hidden from sight!).

The bacteria that do these transformations require air to work. They are aerobic bacteria, or good bacteria. These bacteria can live in a fish tank when there is enough aeration, but most of them will thrive in plant beds. It is absolutely essential that the plant beds are not continually filled with water. Lots of water equals no air, and the good bacteria will die. They can survive and thrive in occasionally-flooded environments. This is what happens in an ebb and flow setup: Ammonia rich water floods the plant beds and then drains out. Lots of moisture containing Ammonia is left behind. And Ammonia is food for the bacteria. They will thrive on it, and process the Ammonia into Nitrites and then into Nitrates. No elements are lost in this process, the same amount of Nitrogen that is in the Ammonia will come out as Nitrates.

The third step is done by the plants. They thrive on Nitrates and their roots are perfectly adapted to removing these Nitrates from the pebbels.

Chemistry: Ammonia to Nitrate

In Chemistry, Ammonia is one Nitrogen molecule with three Hydrogen molecules. Nitrate has one Nitrogen molecule with three Oxygen molecules. Bacteria extract energy when they change the Hydrogen molecules for Oxygen molecules, and this is the energy that feeds them.

Bacteria in the Nitrogen Cycle

  • Ammonia is converted into Nitrites by the Nitrosomonas sp. bacteria.
  • Nitrites are converted into Nitrates by the Nitrobacter sp. bacteria.
Few aquaponics resources are as important, and as invisible, as this Nitrogen cycle. Don't ignore the bacteria, take care of them and let them thrive. Your plants will reward you with incredible growth, beautiful and healthy produce and great health. And your fish will be happy, without ever needing to replace the water. Tip: another often overlooked item in aquaponics resources are the trace elements.