JennM;939246 wrote: What Eric said.
Do you know what caused it? Is that a new acquisition? Usually that funk spreads to other Euphyllia sp. (Torch, Hammer, Frogspawn). Occasionally to other corals but usually stays within that family.
It looks like it's in the sand - is that where you keep it? If so, I'd move it up into the rock work after you've pruned/dipped it. It's possible that the sand is irritating it, they prefer to be higher up, in my experience.
Hope you save what's left - Euphyllia are some of my favourites.
Jenn