Are you sure that is not fire coral?
If it is, it will re-occur in two weeks.
When pivoting upside down to look at a sea horse under a coral head, I put one knuckle on what turned out to be fire coral. (At 60 feet+ any color is pretty much gone.) Stung quite a bit that afternoon, but a few beers and very spicy Indian food put out the flames, which never returned.