Mite off is a waste of money if you want to treat your snakes for mites (and I would recommend to treat your entire collection not just one snake) you need PAM - Provent-A-Mite http://www.pro-products.com/miteandtemp.html (this will treat all stages of development of mites)
Now also keep in mind that Wild Caught BP does not = mites, since mites are not found in Africa (Ticks are however). So if your BP has mites this means that the mites come from the source where you purchased your BP.