Thank you for the information on the scales. The scales might be a big clue to what is going on. There is a condition called scaly leg mites some chickens get. There are really tiny mites, so small you can’t see them, that work their way under the scales on chickens legs and feet. This is irritating to the chicken’s skin, and crusty stuff can form under the scales, causing them to lift. Are you removing scales because they are lifting up insteadof laying down nice and flat on the chicken’s feet? If the scales are lifting up and maybe even looking a bit crusty, your chickens might have scaly leg mites. You can soak the feet in warm water with epsom salts, or if you don’t have epsom salts, a tiny bit of dish soap. Then gently scrub with a soft brush like an old tooth brush. Gently pay t lhe feet dry and then put vaseline or some cooking oil all over the whole scale area. Since your chickens have toes that are already turning black, you might want to skip the scrubbing part. I don’t know for sure that this is the problem, but you might want to try it. Good luck, and let us know how it goes. You would need to repeat the treatment again in a couple days. I’m not sure exactly how many treatments would be needed.