I have a 135g and want a stingray really bad, but I have 6 (7") rbp and 2 5" green severums and a 5" jack dempsey, they all have cohabed together for a month or 2 now.
Well ya can try anything ya like but be prepared to lose some rays. Plus it would be hard to keep the water pristine as the rays require, with the filthy RBPs in the tank.
Ya, I'm going to save my money, and maybe make a dir 5x5x2 tank, when I have the time and money. Thanks everyone for your help. And no, I try to keep the piranha well fed on nonlive foods so they can coexist with the cichlids.