I went to the site of mypetchicken.com but couldn't find DE or diatamaecous earth. I know it is sold in garden/plant grade in the garden supply departments of stores. But, although it is easy to find & commonly used, it does contain 85% silica. Food grade DE is not that high, as silica is linked to tumors. I use the following homemade recipe for my chickens & have only seen lice when I forgot to refill the tray for about 4+ wks, we live in the woods with lots of critters roaming around.
HOMEMADE NATURAL CHICKEN DUST BATH
1 part wood ash (from woodstove or wood burn pile)
1 part sand
1 part road dust (fine dusty dust)
1 part DE - diatomaecous earth
-the last 2 ingredients can be substituted with 2 parts Stall-Dri from your local farm & feed store (it contains bentonite clay & DE with only 1% silica). This is what I've been using this year. Also, I toss some on the coop floor once in a while & in each nest box. Stall-Dri rids moisture, odor & the pests.
Mix it all together & put 6" in a kitty litter tray (meaning to try one with a dome lid for cats, but just use the tray now). Keep the tray in a dry area & available to chickens all of the time. They'll do the rest.
If you find any mites, lice or clumps of lice eggs (especially on their rump feathers) or the eggs on their skin or base of their combs, just apply VetRx & again in 10 days for at least 2 treatments. VetRx for poultry is great for wounds, frostbite on combs, & others problems. It can put in a spray bottle for ease & it is not harmful (maybe even helpful) if it gets in their eyes, mouth or nostrils. I do everything I can "natural & organic." Good luck with that.