Not sure if this for me or the person from France. Either way, I took every precaution I read about before I ever put my flock in the coop. You can read all that I did at the start of this thread. I am extremely paranoid about bugs, and now have to take a shower every time I go out there with them, because I cannot stop itching when I come back in. I feel 100% defeated here. I know people say it is not a reflection of a person's care for their chickens, but I have been so careful. My friends tell me my chickens don't even know they are chickens because I pamper them so. Anyway, I'm not sure why all of my preventions failed. I have several friends that have owned chickens for years and have never had a problem with bugs, and I am far more diligent than they are. I hope this reply does not sound hostile, because I do not mean for it to. I am just so upset about it. And thank you for your suggestion. I put the wood ash and charcoal in their dust bath earlier this week.
@Birdwatcher804 I'm pretty sure that was for the person in France and in no way was meant to be a reflection on any one's care, either in France or your coop.
I feel your frustration and disappointment.
You have not failed. It is simply life. There are mites in this world. There are chickens.
One person's place, who is less tidy, never has problems, but then another persons is overtaken.
It has so many elements to it....the kind of wild bird flocks on the property...the kind of underbrush...weather...luck.
Also, many times those that appear to be doing okay have a silently lurking problem which will arise when conditions are right. It truly is the perfect storm.
What you can't control is the wild life bio in your immediate area or weather patterns, and that has a lot to do with the factors of infestation.
Good cleaning, herbals, etc., can hold things back to a point. But if you keep birds in the same location for any length of time, with wild life abundant, stuff happens.
@JaeG has some really good old timer recommendations. Neem oil painted on roosts and elemental sulfur.
Sulfur was the old timer treatment before the permethrins. It is actually being re-introduced as some mite populations in certain areas (of overuse) are growing resistance to the permethrins.
An old trick is to put sulfur in a mesh bag and hang it under the roosts near the entryway so that the birds brush against it every time the enter and exit the coop. It acts as a self duster.
But it is NOT your fault. It is chicken keeping.
I personally burned a coop down...full of my very first flock...from a flood lamp left inside to help them stay warm as I had just integrated them to the coop then an especially early wicked cold snap hit. I learned a powerful and sad lesson from that.
Since then, I've re-established my flock and have over the years suffered Infectious Bronchitis (learned to improve my standards of isolation for newly purchased pullets), Northern Fowl Mite infestation (got behind my coop cleaning ritual when helping MIL into assisted living, hard to catch up when you get behind), turned down a broody Silkie purchase because she had scaly leg (Yes, I can be taught), only to have the other earlier purchase (from same trusted breeder) die from apparent Marek's (after passing a month isolation).

I'm ticking off calendar dates to see if anyone else shows symptoms. (Thus far, week 12, and it looks like I'm okay).
I've faught hawks (put up netting), racoons (lock up tight every night now), and rats (ongoing war...I think I'm ahead at this point...they went to the neighbors
So if you want a trouble free hobby, take up something like knitting (only I can't knit). Animal care will ALWAYS have ups and downs. It is literally the nature of the beast.
There is a time however, between tinkering with issues, when all is well, the eggs are coming in, the birds are happy, and you drink a cup of coffee with your fresh egg omlet...chicken keeping is good....it is very good...and it is worth it.
Soldier on. You are doing fine. Learn and grow with your sweet birds.
LofMc