Is it on only one rock? Can you take the rock out of the tank? If so, and there are no corals you really like on it maybe a freshwater swim for a few hours kill it all, I don't know if peroxide would kill them, or maybe just get a different rock. Throw this one out or trade it to a LFS for credit or see if they will hold the rock with some butterfly fish for a few weeks. My LFS will do a lot to help out a good customer. Just a few ideas.