I need help identifying these algae that is growing over one of my live rocks and starting to kill some of my coral. It's a tough leather-like algae. I pulled some off but it is too difficult to peel it all away. Not sure what it could be but it is continuing to grow. Any help would be appreciated. I hate to get rid of the rock but I'm not sure what else I could do. I have other corals that are growing on it.