I had a similar thing happen - completely infested, rocks, sand, in the overflow... everywhere. On the plus side, it's a good excuse for a bigger tank.I introduced a pink tip majano with a frag and that turned into a few dozen, which turned into hundreds, etc.
The rock and corals were infested with majanos. Hundreds, even thousands.
I tried a couple different butterfly fish, several matted file fish and nothing seemed to work.