I've heard Kalk can work, lemon juice, or some of the Aiptasia killing concoctions. Never had Majanos myself, only Aiptasia, which Berghia did the trick for me, wiped em out. Unfortunately I don't think Berghia will eat Majano...maybe peppermint shrimp? Someone else can confirm...best of luck.I don't think they are majanos... more like green polyps, buttons. Here is a shot of the rock they came in on, better look.
What weapon would you suggest?