My understanding is sharks can be pretty hard to keep. Stingrays need a lot of open sand, so maybe a couple if rock columns. Remember it can be hard to keep a CUC with predators, as they eat snails and hermits and other inverts. Triggers run the gambit with some being much more aggressive than others. My Picasso trigger is the boss of the tank, but not really aggressive except at feeding time. Other triggers can actually attack their tank mates and I got rid of a very mean pinktail for just that reason.