Hmm. I have this happen sometimes but usually only see it once or twice. Since I put the fine sand in my tank it gets covered on the loaches and the cory's. The cory's seem to be doing it bc the sand sticks to them. The loaches do it maybe once or twice but not very often. I only notice it happen when I visually see sand on my loaches. I have treated them for parasites, gill flukes, and tried stress coat a few times. I don't usually see it so often, so I don't worry about it. Now that I think about it, I will pay more attention. If anything, I see this happen to one loache one time a week or so. It doesn't seem out of the ordinary. But I will definitely pay more attention.
All your loaches are belong to me!