I have six in a heavily planted 12-gallon with a couple of nice caves for hiding, and they do just fine. There are bouts when it seems everyone's got nips out of his/her fins -- so yes, they are nippy. Right now, everyones looks to be pretty much intact. I've had this school for about 10 months, so they're really used to each other. You'll have 4 times as many, so I'd recommend the 55-gallon. Mine share their tank with 4 otos and gobs of MTS. They never bother the otos, other than one will occasionally "swish" by a grazing oto at top speed, but I've never seen one of the otos budge. All in all, I'd say this is a happy tank, with contented occupants.
