I'd like to avoid completely stripping the rock, but it may come to that. I've had the rock out of the tank several times and chiseled away the GSP covered areas with a hammer and a screwdriver. It's come back every time. This was all complicated by having a really nice Pink BTA that had its foot in a hole in the underside of the rock. Today I gingerly chiseled away the hole and got the anemone off, so now I can abuse the rock as much as needed to kill the amazing alien lifeform.10% bleach solution soaked for a few days will kill everything. Will even breakdown palytoxin if that’s ever a concern.