You can try mixing up a very salty batch of water, that should chase them out, I don't know exact salininty, but I would double dose the salt you would normally use, you don't need alot of water, just enough to put your rock in for a couple of minutes, maybe enough to shake it around with a gloved hand, it should shock them out, and all be at the bottom of your container. I did this a long time ago and it seemed to work. Didn't seem to hurt the rock itself, but chased some of the bad out. Coral Banded Shrimp will eat them also.