D.E. is fossilized algae. to us its liek flour... to insects its like shards of glass. It is used in some pool filters and grain storage but apparently their is a gig difference is food grade and pool grade.
It is also use in special aquarium filters as a water polisher.
It's also called fossil shell flour. Because essentially that's what it is. The fossilized skeletons of ancient diatoms.
What you see talked about here is FOOD GRADE diatomaceous earth, not pool grade. Food grade is used all throughout the packaged food industry to keep bugs out of various dry mixes. It's also used in grain silos for the same purpose. Pool grade can kill you.