Help with mites!

[Mutimbo]

Hi all,
Haven't posted for awhile because everything has been going well. Even my baby retic who went the first 9 weeks in our care without eating is eating like a pig and growing like a weed. Everything was going well until today. Melvin the previously mentioned retic has spent the whole day in his water bowl. I took him out a few minutes ago and checked the water. Small black specks about the size of ground black pepper that I assume are mites. If they are in fact mites, where did they come from? No new snakes in the house or handled elsewhere. Melvin spent 2 months back with the breeder, who helped us get him eating again. We have had him back in our care since mid-Sept. with no signs of mites. We have been using a different brand of aspen substrate for about a month now. If they are in fact mites how do I eliminate them?