IIRC, you arnt suppose to squish them because that'll release spores(mushrooms?) or eggs or something so i would go with aiptasia X. If thats the only one, you could try a bit of lemon juice
^^^Shut off all pumps and use a hose to siphon it out as you scrap it off.That way it (or pcs of it)won't have the chance to go floating around and get lost.