Get it out but don't scrape it in the tank.
Take that rock out, scrape off the aiptasia where it connects to the rock, make sure non of it is left. Rinse off rock with rodi water. If you have a small container put enough saltwater in it to cover rock and see if the aiptasia reappears on the rock before you put it back in.
Actually there are a dozen ways to get rid of it when it is only on one rock I just gave you what I did.
Aiptasia X works pretty good. Just squirt the stuff onto the aiptasia with the syringe that comes with it. Sometimes you might have to treat it a second time
Take that rock out, scrape off the aiptasia where it connects to the rock, make sure non of it is left. Rinse off rock with rodi water. If you have a small container put enough saltwater in it to cover rock and see if the aiptasia reappears on the rock before you put it back in.
Actually there are a dozen ways to get rid of it when it is only on one rock I just gave you what I did.
I just got one on a base rock. I bought Zapatista syringe worked great. It's been days and it had not reappeared