Am a rookie having 24 chooks of 20 weeks age. All appear to be healthy. I bought some DE at a swimming pool place 3 weeks ago, and it was not expensive. 25 Lb bag might have been $15. I used it for their dust bath. So far I have seen no ill effects from them wallowing around in it. It is well mixed in the compost and sand and dirt too, not loose to make a dangerous dust by itself. I also did a small dust bath in the coop in a 12 x 24 x 6" deep box with compost, sand, dirt, and DE all mixed. It is there for rainy days. I am wondering if I should have used food grade, but am seeing no ill effects from what I did as of yet.