I have one hen that I thought was getting picked on. However after observing them and looking closely at the spot where she is missing feathers I am wondering if she has mites? If so, when I treat her, I need to treat the coop too....I have sand inside the coop. Do I remove the sand or just spray it down? None of the others have any signs but I am guessing she just has a bad case?? I have all hens, no rooster so I know it's not from a rooster pulling out her feathers when mating. Any advice is appreciated!