You can kill it however you like, but to leave the rock will leave aiptasia in the tank 85% of the time.....I haven't seen any in about three years.....I just moved my tank and rocks got flipped and turned.....what do I find? They haven't been a big issue for me, and from my experience.....that goes for MOST aiptasia keepers....they CAN sting corals, but just like bubble algae, there are only a select few that have serious trouble with them. It isn't something you want though....your choice what to do.