sulphur!!!
I just found this formula for a dip for mites from a 1956 usda book on animal diseases. The page is referring to "parasitic chicken mites", including red mites, scaly leg mites, northern fowl mites, depluming or body mange mites.
"Sulfur has been used for many years. The treatment of individual birds with powdered sulfur is satisfactory if liberal amounts of dust are used and if application is thorough. Dipping the birds in sulfur baths is laborious, but the results are gratifying. Dips may be prepared by mixing 2 ounces of finely ground sulfur (325 mesh) and 1 ounce of powdered soap or detergent to a gallon of lukewarm water. The feathers should be wet to the skin, and the head ducked. It is always advisable to dip fowl on warm, sunny days or in heated buildings. Treatment with either sulfur dusts or dips should be repeated as required."
I have added sulphur to the feed, but it is in such minute quantities and since it is so hard to tell if it is working with feather mites. So, tomorrow afternoon I am planning to "dip" all 9 adult birds. Not sure about the ducking of the head. Hope they close their eyes automatically when their head goes under!