I would cook it. Take it out of the tank and leave it sit dry for a few months. then scrub it with a wet scrub brush to get all of the stuff off of it, then let it sit outside for a few more months, and after that you could be ok, or you could just take the rock out of the tank and put it in a bucket of water that is left over from a water changee and set it aside, get some joes juice or some kalk or lemon juice, or mrs wages pickling lime, or use hot water inject the anemone with any one of the above and eliminate them that way. Peppermint shrimp might work too but they gotta be hungry.