Honestly, you really can't get any "cleaner fish" to go in there right now. Your Cichlid attacks everything in there because there isn't enough hiding spaces in the tank for him, so he feels the need to protect every area of the tank as his.

Cichlids need spots that are just their's to feel safe, that's their nature. I have the same kind of cichlid, plus many other's types and the only way, they have ever gotten along is because our tanks are full of different area's for them to hide in. With that, I have been able to put in Clown Loch's, Cat fish, Parrot fish, Oscars and even Kissie fish with no problems. They have now been sharing a tank for several years, sense the build up of slate rock and other decorations. Every one picks a spot that's their's and only defends that.

I'd suggest you do a search on cichlids and maybe get some ideas on how they live and their natural habits, if you really want to add more fish to the tank. Right now as it is I believe your guy will attack anything you put in there, even a snail, would be pushed around.