Hi, I'm wondering what disease this might be in our display tank? For context, we had an emperor angel who died several days ago after experiencing progressive white blotchiness over several weeks (see photo). Toward its final days, it started to lie on the sand bed, exhibit rapid breathing, and eye cloudiness. Since its death, over the past several days, more fish appear to have this same blotchiness (which looks thick and mucus-like), rapid breathing, cloudiness of the eyes, and are laying lethargically on the sand. There are two maroon clownfish who don't appear to have any signs of disease at this point. There has not been any new fish/inverts introduced in the tank for at least 3-4 months and fish are fresh-water dipped prior to placing into the display tank. The tank contains fish/anemones/reef lobster only, no corals. Nitrate is 12 and phosphate is 0.03 by hanna. Any help on diagnosis and treatment recommendations would be much appreciated!