IMO there are a few methods to rid Aiptasia , but I'll go with a sure fire one for you situation . You said you were going to put the rock in a QT and treat from there . If this is possible to remove the rock one or two at a time , all you need to do is buy a Raccoon Butterfly add him to the QT with the rocks and he will destroy them to the core , never to come back again . Just have a plan for the fish after he's done solving the problem .