What do you have in the tank now? How big is the tank?
I would suggest something that will pick at your rocks all day if you really want to get the population down. Everything in my tank eats the frozen mysis shrimp.
I have a Yellow Tang, Yellow Eye Tang, Black Clown Fish, Blue Spotted Toby, Coral Beauty, and a lunare wrasse. I also got a Long Spine Sea Urchin.
If this is in your 40 gallon tank, I would suggest a 6 line wrasse. I would be cautious because they can be punks, but I had one in my 30 gallon tank and he was never a punk. The only dumb thing he did was jump out of my tank and die. :-(
Fish Sticks, the best thing you can do with your dead fish.