How old are your chicks? Do you see them scratching alot? What are you using for bedding? Where are you located? You may want to update your profile with your location so others are aware of what time zone & climate you're in.
Mites are tiny critter, you can do a search in the Predator & Pest forum for information or look it up on the internet - bird mites. If you run you hand in their bedding, if there's mites you'll feel them crawling on you. You can check their vent, under their wings moving their feather ... Watch for any tiny crawly critters on their skin/feathers.