It looks like they are spreading to all different rock. This will not go away and if those are what you can see I cannot imagine what is there that you cannot! All of them must be killed. The best way to get rid of them is to take the rock out and sprinkle table salt on them. They fall off the rock when you do this. I have not had luck with any of the aiptasia remedies available.
That is truly amazing. maybe he can just call it a species tank and leave them be to spread out. They really are beautiful creatures, but if he is looking to do anything else they really need to go. I would be tempted to pull everything out and start over with a cleaned sterilized tank and all new rock and sand and filter medium myself.