i just finished treating my BP for mites that were also underneath her scales, unfortunately she brought them home from the pet store..
i used a pesticide called Sevin Dust, the 5 percent dust at the recommendation of the local reptile rescue. she has used it to get rid off mites off of her snakes when she brought a rescue home and all of hers were infected after that.
you can find Sevin Dust at lowes, walmart, orchard and you want to make sure you get the 5 percent dust. what you do is pull any toys, rocks, substrate, and hide out and place in plastic bin or plastic bag. if using bin, line the rim of the bin with some kind of vegetable oil to prevent escape. dust heavily on all of the stuff and seal it up for bout 1 and 1/2 weeks or 2 weeks because it doesnt kill the eggs but if you leave it for that long the eggs will hatch and it will kill the new mites. now, clean out the bp's home with bleach water and rinse really really well to get all the bleach out. place paper towels or clean pillow case on the bottom of the home and put a couple properly size cardboard boxes in for hides, as well as a water bowl.
next step, oil your hands with vegetable oil and allow your snake to slither thru your hands, coating it with the oil, but not soaking it so its dripping off. get some on its underthroat and a little on the very top of the head but none in the vents or nostrils. place it back into its home and let it be.
the oil will sufficate the mites and not hurt your snake at all, may cause a crappy shed, but mites wil do that anyways. you can repeat the oil treatment several times, bout 5 days in between each treatment. you can also bath your snake in between treatments just to wash away dead mites but you dont absolutely have to.
after 2 weeks of all the stuff from the tank sitting in the dust and the mites on your snake being killed from the oil treatment, rinse all the stuff and shake out the substrate and place back in home, removing paper towels or pillowcase and card board boxes and your snake will be good to go! mites all gone!!!!