If it's just on his back - not anything on his face or around his eyes - don't treat him with anything. It's more likely to be an allergy, hot spot, or a shampoo reaction or something. Just a good deep bath with a mild shampoo and a good rinse and watch it.
If it is mange, Revolution is the best treatment at this point. Thank God, the older dips are no longer being used. They're awful stuff. But tincture of time, and good food and care, work on demodex just as well (and almost as fast!) as Revolution. Demodex mange is a stress reaction (all dogs have demodex and it only goes nuts when they're really stressed or their immune system is down for some reason), so removing the stress usually fixes the mange. Sarcops typically needs treatment, but sarcops is almost unmistakeable because the dogs are just tortured by it. It's unbelievably itchy. If he goes nuts when you touch it, and it's also on the edges of his ears and the borders of his body (elbows, etc.), I'd suspect sarcops and do a Revolution treatment.
Oh, and worm the heck out of him. He's got that wormy look.
"Purebred" is a bit wishy-washy in most US-bred pit-type dogs. The UKC registers APBTs but the vast majority of the "pit bulls" in this country are not registered and certainly may have other breeds in there. He looks purebred enough for me to say he's a pit bull, and he's the right color.
