That's mostly what I'm concerned about. My knowledge of Stringrays thus far is nil. I'm hoping I'll read about a hardy ray that can hold it's own -if need be- against the Dovii or Sharks. I'm probably going to trade the RTC off so I won't have to worry about him. I want to add some exotic Plecos as well. Well perhaps I'll trade the rays for Plecos.
Believe it or not, my larger Black Shark rules the tank as of now. It was originally their tank and when I introduced the Dovii, the shark immediately took a piece of the Dovii's tail.