I think it's leaf coral taking over - advice?
 

I started my tank in 2004 so it's quite established. Always had some good luck but what must have been either dormant or hitchhiked in is a plate coral and it's blanketed one entire rock and creeping onto the next. I've been watching it and finally must decide what to do with it. I am contemplating taking the rock out and killing it off and then replacing the rock once clean. Suggestions? I'm not sure anyone would want it as it is quite evasive. My tank is a 65 g mostly easy mushrooms and fish. I keep it pretty simple well as simple as salt can be lol.

I tried to attach a photo- it's brown and probably 8x8 inches covering a rock

IMO, I would isolate and remove the rock from the tank before it has the chance to move on to the next LR. The only thing is it may already be on the LR, if purchased at the same time. To me I wouldn’t risk it spreading to all your rocks.

Trade the rock to LFS or hobbyist, that's easiest.

Otherwise slowly chip away and toss it.