In my experance, red tail sharks and ranbow can be a bit aggrasive. I have at this time a red tail shark and a rainbow shark in a 75 with a green terror, pearsei, common pleco, danios and a blue crayfish. Lots of decerations. the 2 sharks chase each other around sometimes and leave the other alone. They never bother the other fish.but that might be because of the tank size and lots of places to hide or that they are alot smaller then the others (sharks about 5 in)...lol
