HLLE can be a direct result from stress, poor water and especially diet....even though a fish maybe nice and fat if it's not getting the right nutriants HLLE can develop especially with tangs which need alot of algae in their diets...feeding it the sea veggies and alage pellets along with some meaty foods everyday is a good start in preventing any further spread. I'm currently nursing back to health an Emperor Angel which is a LFS rescue with HLLE and had poor coloration. After a few weeks of a good balanced diet consisting of Rods, Larrys products, clams on the half shell, PE Mysis, fresh Nori and fresh Ulva, I collected at the beach, its colors have dramatically improved and HLLE is looking better, but I dont expect it to fully recover because most fish when they get it will be left with some scar tissue....GL