Can you grow algae in your aquaponic tank to feed your fishes, it can be tricky, but not impossible. Here are a few basics so that you can determine if this is something that will benefit you. Where there is fish and filtered water, there will be algae. If you can consistently cultivate a large enough supply of algae, you can theoretically create an entirely self-sustaining aquaponic system.
Even in the best of circumstances, it is difficult to cultivate enough algae for your fish to live off of. In an aquaponic system, it is especially problematic, because the plant nutrients that the algae would normally feed on are being siphoned away by your terrestrial crops.
Limit the number of crop plants to ensure that there are nutrients for the algae to feed on. Insert a box with plastic grating, such as a milk carton or berry container, into your water tank to give the algae a surface to grow on.
Cultivating enough algae to feed your fish may prove to be a challenge, so make sure to keep the fish food handy until you get the balance right. With a little luck, you'll have a self-sustaining system in no time.