https://www.tractorsupply.com/tsc/product/y-tex-gardstar-garden-poultry-dust
They sound like the mites my coop had and permethrin poultry dust product worked very well. I treated the coop 3x, each 7-10 days apart and it killed all the mites. My coop had a terrible infestation this summer. They were literally oozing out of the coop's crevices. Do a deep clean (remove all bedding) and sprinkle the dust down, then replace the bedding. Make sure to put some on the roost since the mites crawl onto them at night while they sleep.

