U can buy aptasia killer or joe's juice product and inject it or u can save money and take the rock out and get a sharp knife and pop it off. Don't try to smash or scrape it off cuz it will just grow back. If u get a sharp knife and get under the stomach/foot of it it will pop off. It sticks/sucks on like a mushroom. Be careful too cuz sometimes it will squirt at u and u don't wanna get anything in ur eye. They come off easy though.