Twigg, we put it IN their feed, so it must be food grade. I also use it IN the nests to keep out bugs and in the dust wallows and ON the birds, so I don't want them breathing it in. The silica in pool grade DE is 85%, but in Food Grade, it is about 1%.
When I have DE, the first thing I do when I open a bag of feed is put a cup or two in the bag and stir it around to kill any possible bugs that may be in there or that may crawl in there later.