Duckweed
Duckweed is a little wonder plant. It literally grows like weed, but it is very useful. The miniature plants float on top of the water. They remove excess minerals and nitrates, thus help to clean the water. Duckweed also happens to be very rich in proteins. Tilapia love to eat it. You can raise tilapia solely on duckweed. I feed mine pellet food, but always throw in a handful of duckweed. This stuff is reproducing so quickly that you’ll never run out. Under ideal conditions, duckweed doubles every 48 hours. I haven’t quite achieved that sort of a growth rate, but I also have not created the ideal conditions either. My duckweed container only gets about 3 hrs of sunlight, the water in it is not oxygenated or in motion. I pour in the waste water of my swirl filter once a week to provide nutrients to the duckweed.
I purchased a flat bowl as a growing container for my duckweed. I wanted to optimize the surface area versus depth since duckweed floats on top of the water. No need to have more than a couple of inches deep water for that purpose. It took a while before the colony established like you can see in the photos above. I think the water chemistry wasn’t ideal in the beginning. Duckweed also prefers warmer water temperatures around or above 70F. Another nice thing about duckweed is that it dramatically reduced water evaporation. Compared to my tilapia pond, I only need to top off water every 2-3 weeks for the duckweed. It may lose 1 to 1.5″ or so in that time. My tilapia pond loses about 12-14″ in the same amount of time, if not more.
The reason why I am growing duckweed in its own container is that the fish would otherwise eat it all in one sitting. You may also notice some algae growth with the duckweed, especially when the duckweed isn’t covering the entire surface of the water, yet. The sunlight can then reach the water surface and algae grow rapidly. This doesn’t really matter, though. Just scoop the algae up with the duckweed and throw it into your fish pond. Tilapia love both, algae and duckweed.
I had initially added a duckweed float to my fish pond. I built this from PVC pipes, four 90 degree sections and some bird netting to keep the fish from eating the plants. The bird netting is drooping into the water to provide some space between the duckweed and fish. However, several times I had to fish out tilapia from this contraption. They must like this so much, that they frequently jump into the float, but can’t get out. While they are in the net, they’ll have a feast. They also constantly suckle on the netting and somehow manage to decimate the duckweed despite all of my efforts to prevent it. I finally gave up and placed that round bowl outside and just scoop in the duckweed from there instead. I left the float in the pond, just to keep the fish busy. I had another thing in mind for that float. I was thinking, if the tilapia start breeding and I happen to find some small fry swimming around, I could quickly scoop the fry up and put it into the float, keeping it safe from the larger fish. So far, I haven’t seen any fry, but I am still hopeful. Although, I noticed a couple of smaller tilapia and I keep wondering,if these are some lone survivors of some recent offspring somehow?!