Do NOT get your DE at a hardware store. If you ever feed DE to help possibly decrease parasite risks, it should only be human food-grade DE, preferably freshwater. Using garden or pool DE is harmful as it's a way different sharpness and not at all recommended for consumption.
DE is used to help control worms hopefully, but will not prevent them totally. Only a worming program will really do that, and then it doesn't even prevent all worms. It just decreases the numbers that might be in your bird for a while.
Worms, in the intestines, literally borrow into the sides of the gut. For every place they burrow, a scar eventually forms causing a lack of digestion in that spot. Additionally, any time the protective lining of the intesting is breached, you risk undigested foods and proteins entering the bloodstream o f the bird too early and causing health issues. Nevermind all the nutrition they're literally stealing from your birds. So that's why I personally recommend a twice-annual worming with a broad spectrum wormer, and then using DE in between in their environment.
I like to avoid chemicals whenever possible. But as strong a 'naturalist' as I am, my many years with chickens and livestock have taught me when a few chemicals are really worth using.
Use DE, but always food grade, and then worm 2x's a year anyway.
By the way, i've used DE in my chickens' food ages ago for a number of years. I found that 'then and now' are about the same because of my worming program. Because I only used freshwater human-grade food-grade DE, I had no problems with the birds using it less than 2% the weight (not volume) of my feed. In fact, I used to be chided about using DE and more natural products.
Not so much now.
