Be really careful with DE. I was really paranoid about getting mites so I was putting it everywhere including their dust bathing holes. When they dust bath, they kick dirt right into each others faces. They could move. But they seem to like to dust bath right next to each other.
Well, I had two birds develop a respiratory condition. Treated with antibiotics to no avail and eventually lost both birds. A necropsy done by students at UC Davis showed they have inflamed lungs from inhaling silica or DE.
I can only guess that I put too much DE into their dust bathing holes and they inhaled it as they dust bathed together. That was 6 months ago and I still feel just awful. They were BEAUTIFUL big Buff Orpingtons.
I've done a bit of research and there are some who say that DE is not necessary in dust bathing areas. But I also know that LOTS and LOTS of people put it out without issue. So I'm just saying to exercise some caution. A little goes a very long way. Like a teaspoon worth in a BIG dust bathing area is probably plenty to keep mites at bay.
I don't want anyone to go through what I went through, holding their beautiful BO hens in their lap while they gasp to breath. Just heartbreaking.