So I'm keeping the oscar I got in the 75. I would like to add a tankmate or two for him. I don't believe that there will be aggression issues, because the oscar has pretty bad HITH right now and just kind of swims around and hangs out. He does not show any aggression towards the pacu he is in with right now. He is about 9 inches long right now, so any tankmate would have to grow big enough to compete with him. I can grow it out in my 55, so buying small is not a problem.