Use this. Get it at your local feed store.
This is what I use on my never ending fight against lice/mites. Kills then almost instantly. Just shake on and rub down to the skin level around the affected areas, also, you can fluff get out after a few minutes to remove the dead insects.
Prozap (3 Pack Garden & Poultry 2-Pounds Each Poultry Dust https://www.amazon.com/dp/B071XQDDXZ/ref=cm_sw_r_awdo_navT_g_HE9T0RYRPWESJEJY30WS
If you are referring to using diatomaceous earth, I have had zero luck with it for lice and mites, not saying it doesn't work for some, but didn't for me and I lost chickens before I found what did.
I would recommend to deep clean the whole coop. If you aren't against it, I would use permethrin dust for poultry. When we had a bad outbreak, we deep cleaned then lightly dusted the entire coop, especially in the corners, nesting boxes, roosts, etc. Then I took the dust, flipped the chickens on their backs, then powdered under their wings, their tushes, and carefully around their heads. You dont want powder going every where, it is a pesticide. I would wear protective eyewear and a mask, but just try not to puff it excessively around where it can be inhaled by yourself or the chickens. Its the only thing that completely got rid of it for our flock.
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Just note, this stuff is lethal for cats. I dont know why, but its what is says on the label. So I always wear something I can bag up and wash, even though i dont have outdoor cats. Never wanted to test with just walking in the house.
I use this: