Do you have a food scale? You'd add 1 lb of DE to 50 lb, but I dont worry about doing that precise of a measurement. I just add a cup or two to the feed to kill any bugs that get in and keep the moisture out. When the feed is about half gone, I may add another cup or two to the remainder.
I've got a box full of DE that I bought from Home Depot several years ago. It was for pool filters I believe and I used it for a DE filter in my reef aquarium when I had one. Seemed to work fine for that with no issues the whole time I had my aquarium.
"Pool filter grade diatomaceous earth has been heat and chemically treated and will poison an animal or human who ingests it, so it is always of utmost importance to only obtain food grade diatomaceous earth to use in and around your household. "
Thats curious still...
Especially if I used it in my aquarium with no ill effects!
I think my 13lb box from Home Depot cost $13. If it is heat and chemical treated... you would think that it would cost more than "food grade" that hasn't been treated?