So, sounds like lice?I saw one very tiny almost translucent white bug run on a chickens belly.
Not sure you even need to treat the coop.
If you have roost mites, then the coop needs to be treated, best to use spray and soak all the cracks and crevices.
Good post about mite ID by Lady McCamley:
https://www.backyardchickens.com/threads/my-chicken-has-mites-now-what.1273674/page-2#post-20483008