Wow, David, I'd call that a mighty successful food growing operation. Do you feed your tilapia anything else? I've discovered that mine love the algae from our decorative ponds, by the way. Great to stop cursing that stuff as I throw it on the compost pile.
OK, I'm going to add in some fish emulsion, and ask my buddy Nate if he can bring me some of his favorite varieties when he comes through town to deliver our first load of towers(exciting!!!). Nate, do you have Texas sized duckweed (would that be Donald Duckweed?) like David uses? I've also heard there is a gorgeous red variety....
Thanks everyone for your help! I'll let you know what happens
After some debating I decided I wouldn't grow duckweed for fish food (in addition to worms), instead I would grow fast-growing high-protein green plants that the fish would like to eat. I hear some love watercress, for example. In the end I decided it would be easier to grow that than maintain duckweed, though I have no idea yet if I will be able to grow enough greens for the fish! I assume the main advantage to duckweed is how fast it doubles in size/weight?
It is important to note that if you want to harvest anything from a system, you are going to need some input. If you expect to get the fish to grow fast, you will need to feed pellets along with supplemental feed and if you expect enough excess nutrients to also grow veggies as well as fish feed, you will be needing to add something to produce those nutrients.
You don't get to have an aquaponics system that only produces fish, veggies and fish feed all for harvest. Something must go in in order for there to be much to harvest. The sun and air can only add so much, at some point you must feed the fish or add something to feed the plants in order to expect the system to feed you.
You need to check in with mark in fl. He has some great duck weed going.