Any fish in the tank?
Does the food ever make it to the bottom of the tank? I was told by someone that uneaten food(flakes, pellets, etc) is poison. If it touches the bottom of the tank, it was too much food or given too quickly.
I think these outbreaks have to run their course. Mine took a few weeks for it to start going away...I fed 2-3 times a day with a lot less food, 2-3 water changes a week, only had lighting on from 8am to 4pm.
I vacummed out a lot of sand that had it on it, but not sure if that was the right thing to do.
Dana