Nabiki
Quail Geek
DE is basically silica. It's abrasive, so I wouldn't put it in their sandbox. It can cause irritation.I think they are just molting (a couple other hens are also losing feathers) but have been giving them DE in their sandbox every day, and vinegar in their water; seems to be helping. Everybody is eating and laying normally, so I'm just going to keep a close eye.
I did buy the vetermycin just in case - if anybody gets worse, I'm going to use it...