I called 3 avian vets, and was told to use DE, so that's what I did. just on the backs near vent and a bit under wings. I am so paranoid of respiratory issues. I am watching them closely, but if there is a problem, Im not sure i can actually do anything for them. I let my cochin dust bathe in sand and put some on her back so I wouldn't aspirate the chicks, and cleaned out the brooder. Vet said to re treat in a week. They said DE is the only thing they would use on day old chicks. I still may go get poultry dust for my large coop. It isn't an infestation yet, so hopefully the DE does the trick. I haven't seen any of my large birds scratch at all. I think Lavender got it while she was broody and gave it to the chicks, then when I put the chicks together in the brooder they gave it to each other. I am treating everybody anyway.