Just noticed the age of your chicks, might be having a problem with Coccidiosis which Corid will turn that around ONLY if you are extremely diligent by isolating the youngsters. We had a short lived outbreak of that darn stuff during a very wet spring. So young chicks less than 16-18 weeks...
Get some Corid, and depending on age of your chickens, get some worming capsules, or drops for water supplies. Follow directions exactly and everything should be fine.