well my bloods have small black dots on them also, but they arent mites. mites move. check your snake closely. it could be just the natural coloration that the snake has. as far as substrate, most people will say that newspaper is best but i have started using shredded white copy paper. it looks cool and the snakes love to weave in and out of it, espescially balls and redtails.
as far as getting rid of or prevention of mites, from what ive been told "provent-o-mite" works best if used properly. there are cheaper and just as reliable options out there but its up to you as to whether or not you wish to use them.
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2.1.1 Blood Python
1.1 Redtail Boa
1.0 Dumeril Boa
0.1 Carpet Python