It's aiptasia most people see it as a pest I'd personally kill it, it will spread very rapidly and sting corals. It's very hard to kill and there are many methods
I'm sure someone here can send you a thread fir getting rid of it. Try turning out all the lights in gbe room and when it gets pitch dark is when most of the life really comes alive use a flashlight to spot shine in holes and cracks.
Kill that aiptasia now while you can after it spreads it could pop up anywhere
cheers:$