I needed to buy a large quantity of pots for the plants I started in the greenhouse. So we went to an organic farm and supply. Found the pots I wanted and a few other items. Then got the tour of the greenhouse.
They had basil, tomatoes and romaine lettuce planted in boxes filled with gravel. In the front there was a fish tank with about a dozen talipia in it. They pump the water from the fish tank through the gravel in the boxes. The plants take the nutrients and the remaining water is filtered and pumped back into the fish tank. The fish are fed organic cat food because they cannot find organic fish food. In a couple of more months they will pull the fish out to eat, clean the tank and then put the bunch of minnows into the main tank. It is a neat system.