I bought a 25# bag of DE at a swimming pool co for use in chooks dust bath. I mixed it thoroughly with dirt, compost, and fine sand. They love it, and have used it for around 3 weeks with no ill effects. Still, I wonder if I should have used food grade and if so, is it because they might eat some. I made a dust bath with the same DE for inside coop too in a 24 X 12 X 6" tall box for rainy days. I know if included in food for livestock, it should be food grade.