These chicks are 5 & 6 weeks old, their coop is warm and clean, clean water, grit for the egg they love, medicated feed, all clean. I clean out and add clean shavings every other day, or now that snow is on the ground, add a layer to the floor. All have been vigorous and active, they eat, drink and take in grit very well. Last week one was fluffed up and sleepy, I immediately added Corid to their water and using a dropper treated this one. It died overnight. So for 8 days now the others have been on the Corid, all healthy and doing well. (I sit with them for about an hour each day to observe). This morning another is fluffed up and sleepy, I know it will die too! What is going on and what else can I do? I have never lost chicks, this coop was thoroughly sanitized ( I am a germophobe) before they went in, they are warm with no drafts, but air flow above. No other chickens, no access to outside. I am at wits end! I am using 1/2 tsp Corid to a gallon of water, is this right?