X2. I like the Sevin liquid spray for the coop since it gets into all the nooks and crannies really well. I use Y Tex Gard Star Garden and Poultry Dust from TSC on the birds. And you may have to repeat more then once to get on top of them. Every 7 to 10 days until they stop hatching. They are hard to get rid of because you have to keep getting the new ones that hatch and if you miss just a few the cycle just continues.What you need to do is go to Tractor Supply or another farm/feed/garden store and pick up some Sevin 5% Dust. It's in a red container. Dust the birds with it, either by putting some in old nylons and using the nylons as a powder puff all over their body, or by filling a small bag with Sevin, putting the bird in leaving just its head out, and gently shaking the bag so the dust goes all around the bird. I like the nylon method, lol.
Then, clean out the coop. Clean it well. Use a gentle soap and water. Dust everything with the Sevin (the walls, floor, roosts, literally everything), put bedding in and mix the bedding with Sevin. Wait a week, and do it all over to kill any that might have hatched in the meantime, since Sevin does not kill eggs, just adults.
I personally would not depend on DE to get rid of a mite infestation, I just have not found it to be very effective. Possibly a helpful preventative but not to treat a major infestation. Mites can kill your birds, you need to really get rid of them. I also would not call somebody lazy for using an appropriate treatment to get rid of them any more then I would call somebody lazy for choosing another option.
Chickens don't have to be overcrowded, poorly fed or unhealthy to get mites. Wild birds carry mites all over the place and just the fact that chickens live in a coop, bedding on the floor, lots of places for mites to hide, makes mites a possibility. I have never had mites in my current flock. Doesn't mean I won't ever, that's why I check them regularly and have the means to treat if necessary.