It sounds like you're dealing with lice, not mites. Lice are white or off white in color and move quickly through fluff and feathers. They have 6 legs. Egg clusters can be seen attached to the base of feather shafts, IF they have laid eggs. Lice are more of an irritant to chickens than anything else.
If you treated your birds for external parasites, then you MUST treat the inside of their coop as well or you're never going to get rid of them.
Mites are black or red in color, look like pepper and are slow movers or dont move at all. Mites have 8 legs. They suck blood and can cause anemia, then death.
Both lice and mites prefer warm moist areas on a chicken, especially the vent area. Sometimes lice are seen around the eyes of a chicken, taking in or feeding on the moisture from the birds eyes.
Preferred treatment is Permethrin liquid or powder which can be bought at most garden centers or hardware stores. Not only should ALL birds should be treated, but inside the coop(s) as well. This includes removing all bedding, nesting box material, and treating roosts.
Then take all of the soiled/contaminated bedding and nesting material away from your coop or pen and incinerate it.
Once the coop is thoroughly cleaned out, either spray or dust the inside the coop top to bottom including nest boxes.
An easy way to dust the inside of the coop is as follows:
Securely close all vents and doors except the pop door where birds enter or leave from inside the coop. Put a couple of handfuls of Permethrin powder at the entrance.
Get your leaf blower and turn it on full blast and aim it at the small pile of powder at the coop entrance.
It'll look like a smoke bomb went off inside the coop and I guarantee you that the dust will get into every tiny crack and crevice. Any and all hidden/non hidden insects or parasites will be dead or dying.
Wait until the dust settles and the air is clear before opening up the coop. Then add new bedding and nesting material, lightly dust both, then lightly "pat" it down with your hand.
Permethrin powder and/or liquid Permethrin is effective for 28 days after the initial application.
Use common sense as to which product to use. You dont want to treat birds or inside the coop during cold or freezing temps.
It's best to start early in the morning if you're going to spray. You want the inside of the coop completely dried and aired out prior to putting your birds up for the night. You can put a couple of fans inside the coop to help dry it out if you have alot of humidity in your area like we have.
I also recommend wearing old chicken clothes, shoes, wear a mask and if you wish, eye protection.
