I've got some wolffia, just waiting for the weather to warm up. This stuff is hard to deal with, I'll warn you in advance. Being so tiny it gets into lots of places you don't want it.

The other duckweed I have is around 1/8" in diameter. Grows like mad and the tilapia love it. I got my start from a gold course pond in Richmond VA about 5 years ago. The stuff can not be stopped!