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 old, are easily affected by too wet of an environment combined with their food and droppings is the recipe for disaster.  We lost three chicks in a row and then saved four more out of that same population.  It took ALOT of diligence to save them, round the clock drops of ProMoxil, Corid, and B Complex vitamins.  Even had to use two direct undiluted drops of Corid once a day for one chick via syringes straight into their beaks.  But hey, the last four lived and are doing extremely well.