Auqaponics works based on a cycle in which nitrogen is used in the growth process for plants. When these plants are used as food for fish and then digested, the fish waste becomes ammonia (and solid waste and other components). Then, bacteria in the water converts (uses for its food) the ammonia into nitrites. Then, another set of bacteria converts the nitrites into nitrates. This is a naturally occurring process and is something that develops in fish tanks over time (you may have heard of it as “cycling” your tank).
This cycle is the “fuel” for your aquaponics system. This requires that there are enough nitrates to support the plants in your system and enough plants to remove the nitrates so it doesn’t become toxic to your fish.