Donââ"šÂ¬Ã¢"žÂ¢t dip it, it wonââ"šÂ¬Ã¢"žÂ¢t help, it could make it worse. I have this coral in my tank now since I have been in the hobby. Itââ"šÂ¬Ã¢"žÂ¢s one of the first corals I got, I sold a lot of it, it is huge. This has happened to me at least six times, usually when I move the coral to a location it donââ"šÂ¬Ã¢"žÂ¢t like. It likes to be up high close to the light and with enough flow to move the branches around. If it lays on itself and donââ"šÂ¬Ã¢"žÂ¢t move this happens, you get this black (possibly bacteria or dead tissue) and tissue necrosis under it. If you keep cleaning the black stuff off and get it into the proper location, in a few days it wonââ"šÂ¬Ã¢"žÂ¢t come back and the coral will heal up fine.