If you determine that it is scaly mite you will need to treat the entire flock and disinfect the coop. I have heard that Nu-stock is the best. It is reportedly a lotion that smells like Pine Sol. You aslo should dust them all all over with wood ashes
I put vaseline on my chickens legs or triple antibiotic ointment anything that is oil based. It suffocates the scale mites. Then I seven dust everyone for mites and put some in cracks and crevises in hen house. To wash and disinfect is always wonderful but I never seem to have time to always do that. I have also put kerosene on their legs too. But it was what older adults around here said to do and it got rid of them but just idea of it being kerosene worried me.