My Red Tailed Black Shark bullies just about anybody. Only successful tank mates are Killies, and I can only keep a pair to avoid agression among them, corys, and a pleco. He even chases Barbs! Got any more ideas for midwater tankmates? He is still very small and I can't move him into my larger tank until he gets bigger.
The main problem with RTBS's is their high aggressiveness and territoriality. A group works better if you have space. But I'd reccomend at least 5 specimens. My 0.02 