In an aquaponic system, the fish feed is one of the most important inputs.  There is a direct relationship between the feed going into the system and the growth of your plants.  Think about it: You add feed into the system, the fish eat the feed and produce ammonia, bacteria convert ammonia into nitrates, the plants consume the nitrates and grow.  Because of this relationship, balancing the proper amount of feed entering the system is essential to the overall success of the system.  When sizing an aquaponic system, you can use the formula, 20 g of feed per square meter of Deep Water Culture growing area.  Using this formula, you can calculate the amount of feed needed in your system.
Only feed the fish what they will consume in 5 minutes – scoop out any uneaten fish food to avoid unwanted water quality issues.  If your aquaponic fish don’t seem to be hungry don’t feed them. Fish can survive for weeks without feeding.
If you are cycling your system with fish, feeding should be kept to a minimum during the first 1-2 months.  Once your nitrifying bacteria levels can quickly digest ammonia and nitrites in your system, increase feeding levels, again paying attention to how much the fish consume in 5 minutes. We prefer to feed our fish 2-3 times per day, to encourage a steady metabolic digestion rate and maintain a steady amount of solids. As a guideline,  the chart below can be used to determine what percent of their body weight your fish should eat based on their size.