I've had my baby BP for less than a week and I just discovered he has mites

I saw a black speck on his neck a few days ago, dismissed it as nothing, until today the thought of mites popped up in my head. I'd read about them previously in my extensive research prior to purchasing my first BP and all of sudden, it occurred to me that black speck might have been a mite. I examined him again and didn't see the original black speck on his neck, but rather now there are two black specks in the grooves and scales under his chin.

Currently, my BP is soaking in warm water to drown the surviving mites and I'm vigorously scrubbing down his 16qt tub, his future tub, and a free aquarium style tank that I got from the breeder. Then I'm going to spray everything with a bleach-water solution. I trashed all the substrate and I am freezing the rest of the bag of substrate. The wood pieces I am planning to put in boiling water. I wiped down the area where I keep him and I'm going to wash some clothes I've worn recently.

Is there anything else I should be doing? I read that I have to do this for the next 4-6 weeks

AND Where in the world did these mites come from? I've only had my BP for less than 1 week!

I am so sad to see this happening.