DE is diatomatious earth (I'm sure I butchered that spelling...lol). It's basically crushed (into a powder) fossilized matter. It helps prevent mites and lice, because the tiny fragmented peices of matter cut up the buggies (or something to that effect). Some folks even use it to repel fleas on dogs and cats. You need to be certain you get food grade/fresh water DE though, because there is a kind that is sold to put in pools which would most likely kill animals. Your local feed store may carry it, or you can ask if they can order it for you. Sometimes garden nurseries carry it too.
I haven't used ash in my sand yet (although I have a bag of it I've been meaning to try), but I mix about two cups of in my sand box. I also mix it with my nesting material in my nest boxes, and in my girls' bedding in the coop. I have yet to experience mites or lice w/my chickens.
