I bought some DE after reading all of the great things it was good for. I started putting it in nesting boxes. About 6 months later I had an outbreak of northern fowl mites I'm not saying the DE was the cause (of course), but it did nothing to help that situation, IMO. So, now I don't use it because I see no point.
Feel free to check out the links below for some interesting reading. Good luck to you!
Welcome to Backyard Chickens. I have personally used DE and not found it to be helpful in any applications. Sorry I wasted the money but, it had so much PR going back in the day, I was compelled to try it.