Haaaaaa... just discovered this thread, old like brandy, hahahahaha... but I think it is worth it posting, as I have duckweed in my tropical tanks. It won't get sucked up in the filter, it swims on top of the water where there is no movement and it gives very good protection for the babies to hide in.
It grows very quick. So what I am doing from time to time: scoop it out in a tub, sort of quarantine it in a water with some aquarium salt, then rinse it again and put it in the goldies tank. They eat it as a salad snack.
( doing this, I HOPE the dwarf anubias will recover, and the java fern...