thats a big fish for a 55g. let along 2 over 7 inches. i'd recomend a bigger tank and another P. the big one is going to start to pick on the little one.
I would say you need another also. If thats all that is in the tank a 55 will be fine for a while. My first 5 rbs I had were in a 55 untill they were around 7 "s. They were just fine.
