Greg's probablly right on this.
Brooklynella (clown fish disease)- "small whitish spots, spots begin to enlarge and soon mucus and skin begin to sloth off and the affected areas become red and raw with loose scales"
Amyloodinium (velvet)- Rapid gilling "as the infection progresses, the cysts become visible on the fin membranes and body surfaces. These cysts are about the same size and color of a grain of table salt and, especially on light colored fish, are difficult to see." "Infected fish often scratch their sides on the bottom or on rocks, and sometimes shudder or shake while swimming. As the infection progresses, colors fade, a powdery or dusty appearance becomes very noticable as the cysts proliferate, and secondary bacterial infections often develop."
(quotes from "The marine Aquarium Handbook", M. Moe Jr. 1992)