In my experience, you should ditch the cichlids if you want to keep a big black shark. They seem to take exception to cichlids big time. My black shark used to beat up on my balas and tinfoils too, it never managed to kill any, but they never looked in top shape while they lived in with the black shark. It will be luck of the draw rather than anything planned as soon as the black shark gets big. In general with mine, anything small is ignored, anything big is fair game. Oscars are far too variable in my experience also, and could itself cause mayhem with your other fish.