The key concepts here are water flow, fish stocking rates, and plant stocking rates. To reduce energy use, the total head of the system must be as low as possible. This means putting the biofilter (plants component) at a height barely above the fish tank.
Our system involves a continuous flow system with plants in containers. A solar pump pumps the fish waste and water up to the plants. The clean water then falls back down to the fish tank. It is a self-contained system that can grow enough food for a family in an area smaller than a hybrid car!
Fish wastes are excellent organic fertilizers, as they contain many trace elements and are mostly ammonia. The unfortunate fact, however, is that they build up quickly and soon kill the fish that created them (sound familiar?). To avoid a mass kill-off, it is essential to filter the water. One of the simplest and best ways of filtering water is to establish a bio-filter. Bio-filters work by growing friendly bacteria on a substrate, like gravel. The bacteria break down the fish wastes into soluble nutrients that can be available for use by plants and aquatic life systems. By running the water through plants as well, these nutrients get taken up by the plants and the water is returned to the fish very clean and fresh and oxygenated.
By establishing a good bio-filter you can increase the stocking rating of the fish, thus increasing production. On average, you can grow 7 tons of food to one ton of fish waste. For most systems, aim for a 2 to 1 ratio of bio-filter volume to fish tank volume.