i dont think you can worry too much about red mite, once you get it through complacency, you will live to regret it, it is hell.i have had it without bringing new stock in, if one of those hens has one single mite one, once the warm weather comes around they will explode. if your coop has lots of gaps inbetween planks etc, i doubt you will ever get rid of it. i have had to burn a shed due to being unable to get rid of them they were that bad. i have had it in infested level, and it is hell, you come out with them crawling everywhere, through your hair, it sends you nuts.i would powder reguarly