I used to have a permanent 1.2 trio in a 20 long... that seemed to work okay for a little while, but now I have decided to rotate more than 2 females through a single male. It has worked really well so far. I am trying to get away from buying any additional feeders at all.
Here are my current breeders :)
http://i84.photobucket.com/albums/k1...e111/rats1.jpg
http://i84.photobucket.com/albums/k1...e111/rats2.jpg
As soon as I get a rack built, those tanks will be history. :)