i have never heard from any 1 who has sucsessfully kept these as they all seem to die in captivity. and really mess the params in a tank very quickly when dead.....
i myself havnt kept these just going on what i have read else were.....but good luck.
If you filter your water they will eventually die, they filter detritus and the protozoa that live in the detritus. Green water can feed them but most people don't cultivate green water. I use them in a sedimentation type filter to help mineralized the sediment from the aquarium.