Some of my chicks are scratching like crazy at times, like they have fleas, mites or something! I can't see any crawlies, and have been changing the pine shavings daily since I first brought them home. They are about 1 and 1-1/2 weeks old. Can I put DE in the shavings? I have some, but it's not listed as 'food grade'. Or are they too young for that?