How interesting ! worth doing this if it keeps them at bay !
I too have battled this summer, but finally i can say that we are fully clear of them !!
I tried scrubbing everything with jeyes fluid then dusting with diatoms ! -still there !
Then I tried scrubbing everything with bleach ! and a dusting with diatoms ! - still there ( but lessoning!)
Lastly I tried scrubbing with stronger jeyes, left to dry and then sprayed everything in the coup with a spray (from PandTpoultry) called 'mite killer' you must then shut up the coup to keep birds out and the spray in ! after a couple of hours you leave the coup open to 'air' before allowing return of birds. I then replaced fresh bedding with diatoms powder everywhere. After this method I had only very few on the floor only, so I repeated after 5days again and then a week later again. Now I have none !!!
I dont know if this was the continuous use of everything or the spray that worked , I dont care ! but I will continue to spray perhaps once a fortnight and will always have diatoms powder in the coup !
So dont give up, I think a continued attack is what is needed whatever you use !