It is easy to skim over the ways the plants are fed by the fish held in the aquaponic systems. Often the simplistic comment that fish poop feed the fish is used. While this may be partially true, there are a lot of ways places where nutrients in aquaponics systems enter. The main one, of course is from the food provided to the fish. There is very rarely anything else added to the system so the majority of the nutrients in aquaponics systems used by the plants are directly related to the feeding process itself, but there are other sources as well.
One of the major places where ammonia is produced is across the gills of the fish. As they respire, ammonia is passed out. Of course the feces produce a lot of organic solids. Uneaten food will fall to the bottom and rot, again producing lots of dissolved nutrients in aquaponics systems as well. The plants up above, though are not looking to pull organic solids from the water, they are interested in inorganic compounds. The video by Dr. Nate Storey offers a clear look at the way the nutrients added by the food and possibly entering with water changes are used in the system, and why some of them may not be available immediately.
Nutrients In Aquaponics Systems Are Not Always Immediately Available
There are a large number of nutrients required by both the fish and the plants. But often the importance of other “invisible” areas are forgotten. The fish may digest the food they eat, but it takes the tiny bacteria to mineralize those wastes into viable nutrients for the plants. Nitrate, phosphate and many other compounds are the inorganic building blocks that grow the plants. Nutrients in aquaponics systems can be available immediately for the plants, or they might have to go through a number of levels of the food chain before they finally can be used by the plants as useful nutrients in aquaponics systems.