In the Aquarium Nitrogen Cycle, we need to know the processes of NH3, NO2 and NO3. The process of fish waste converting to ammonia is known as NH3. The process of harmful ammonia being converted to nitrite (less dangerous) is known as NO2. From nitrite to nitrate (harmless) is known as NO3. This Aquarium Nitrogen Cycle will occur whenever there is ammonia in the aquarium. So, you need an Ammonia Test Kit to test the level of ammonia in your aquarium water tank.