Since nitrogen is the most important nutrient in fish feed and supports both fish and plant growth in aquaponics, nitrogen transformations are the main biochemical processesin aquaponics. Nitrogen in fish excreta exists mainly in the for mof total ammonia (TAN, i.e., NH3and NH4+), which is then oxidized to nitrite (NO2−) and eventually to nitrate (NO3−) through nitrification . Growth and activities of all system components (i.e. fish, plants and microbes) could be easily affected by environment changes.