I have a maroon slightly bigger and a pair of black onyx in a 330, I introduced them all to the tank within a matter of days and at first the maroon tested them a bit but being that there were two of them they managed to hold their ground and all seem to be doing pretty well, its been about two months now. I will say at first it was a little exciting and my wife did freak but couldn't catch the maroon to get him out, maybe he sensed what was coming and decided to play nice?