I just thought of something else. If you are raising tilapia, they will eat just about any sort of veggie if cut up a little so they can bite it. If you have access to trimmings and left overs of green leafy veggies they will eat it and provide potassium to the water for the plants. Even duckweed taken from local ponds will provide a lot of potassium. You can't get something for nothing, so don't try growing it in your own tanks.