I hate to contradict anyone, but the fact is that pool-grade DE is heat treated, which is what makes it toxic, and it is deadly. It has nothing to do with where the diatoms came from, but the fact of the heat treatment on the pool stuff that chemically alters the material. Food-grade DE is just the natural product and is very healthy for people and all animals.
I put DE in my chicken feed and heavily in the pine shavings on the floor of their coop, as well as sprinkle it in the timothy hay in their nest boxes. Every so often at night when they have settled on the roost and I come in to check on them I'll bring in the container I keep out there and work a handful of DE onto the back and under the wings of each chicken, including the rooster who I don't touch much aside from that. They all love it and coo afterwards, including the roo.
It can also be given in the feeds of all animals. My 150-pound pet potbellied pigs get 1 Tablespoon a day in their veggies and pellets floating in water, the dogs get it, the cats, etc. It has a range of nice minerals and is somewhat effective as a wormer, most effective as an ongoing preventative when the birds start clean. I had occasion to take one of my hens to the vet, as she was acting very down, and took one of her stool samples from when I had her isolated. The sample and the exam revealed absolutely NO parasites inside or out and the vet was very pleased (and the hen recovered fully).
My chickens like to dust bathe on the bottom of their coop floor, frequently in the space under nest boxes. In our wet climate it is the most reliable place to find dry materials.