Algae creates alkalinity in the water. In fact, when we take a side stream of aquaponic water to our cells of aquaponics the pH rises up to range of 9-10 very quickly. We also raise algae with human urine, but if using as aquaponic fish food and ultimately for plants, care must be taken that source has low sodium diet (salt and soy sauce, etc) as it will raise the EC and salt deposits in soil or roots will impair growth.
Otherwise, algae is great for fish and can be used to control pH of aquaponic systems when the levels drop below 7.0. Fish love the alkaline water and the algae gives them a source of food that reduces stress and prevents them from having to compete for nourishment. We also like the zooplankton, mosquito and midge fly larvae that comes quickly with algae water. A diverse diet is most practical for fish.
Despite being a standard aquaculture feed, fish do not naturally eat soybean and wheat, and probably wouldn’t appreciate that they are often genetically modified grains and legumes. Decomposing grasses, leaves, duckweed, algae, larvae, zooplankton, detritus, bacteria, protozoans is what they prefer. Plus it’s free.