You should be able to spot mites, fairly easy, they'll be little black dots crawling around on your snake. Also snakes with mites often spend a lot of time soaking and you'll see a bunch of them floating in the water dish.
DO NOT USE LISTERINE - it contains alcohol which is very irratating to snakes, look for someplace to pick up some Reptile Relief and bath him in that, thoroghly clean and disinfect the cage throw out the old substrate and put down new and spray down entire cage with Provent a Mite, make sure you get the corners real good, thats were the eggs will most likely be laid. Repeat this cycle again in two weeks then again two weeks later.
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Tosha 
8.13.0 Ball Python (Harry and Fluffy and currently un-named)
0.2.0 Feline (Pippen and Pandora)
0.0.1 Dessert Tortoise (Pope)
7.9.5 Fish (1,2,3,4...)
0.0.1 Frog rescued from pool skimmer
0.0.2 Lizards rescued from pool skimmer