When my hens had lice -- transparent but visible to the naked eye -- I cleaned out (and burned) all the straw bedding in their coop and surrounding area, then I used a bucket of warm soapy water with bleach in it and scrubbed down the entire inside of the coop and the nest boxes. I do this early in the morning so that the coop has all-day to air dry. This might not be a good idea if it's a really cold, icy, and/or cloudy day. Do it on the warmest, sunniest day you'll get in the near future. I then sprinkle throughout the coop some DE and Borax, and put in a light amount of fresh bedding. The next day, or the next day that is nice enough outside that the hens can stay out all day-- I spray a good dose of anti-lice spray that I get from the farm store, making sure to get in all the corners, and a quick spray in the nest boxes. I then close the windows and doors -- quickly, and don't breathe!-- and keep it sealed for an hour. I then open the coop up and let it air out all day. I repeat this pattern every week until the lice are gone. I would do the same approach with mites. Also make sure that they all have access to an area where they can dust bathe.
