Raphael Catfish are extremely reclusive. They only come out at night, and you will nearly never see them around the tank. I have a piece of rock they hide under and I can see them in there.
I havn't seen them out of the rock in the past month or so..other than times I have forced them out by moving the rock.
The pleco, I bought when the turtles were small, and it was twice their size so they didn't bother it. They really ignore it now. Occasionally they will piss off the pleco by scratching it while swimming and the pleco will begin pushing them around, sometimes wedging them in a corner to prove it can still whip them. Still, the turtles ignore this even.
I have had several tiger barbs, and they all wind up dead though. I think the water quality gets a bit out of the range they like and they get sick...then the turtles eat them. I have given up on trying them. I have enough in the tank already.