One of my 3 week old silkie chicks has white flaky skin on its back. Had what I think was lice when I got them two Weeks ago. treated with de and lice and mite spray for all birds that I bought at petco. Treating twice aweek and sprinkling DE in bedding. I have not seen a any more bugs for at least week. Only one has this dry scaly looking skin on its back and top of head". Should I do any thing, why is it like that?