We have 14 black marans and black Australorps we have raised from just a couple days old. They were fed medicated feed for first 6 weeks and kept inside with a heatlamp. At 6 weeks we weaned them over to regular crumble feed and moved them to a bigger "cage" in our barn still under a heatlamp. We had two die not too long after moving them to the barn. Now we just moved them into the large coop with our bigger adult Copper Marans and we just had one of the 3 month old chicks die today...they are in an enclosed big coop that we try to keep clean including their feeders and waterers. After the first two died about a week ago we began Corid and a good liquid wormer in their waterers immediately. We are still treating with Corid and the wormer currently. What could this be that is killing our chicks? They act fine then start being a little lethargic and sluggish then die within a day or two. We are new at this chicken raising and all. Any help is appreciated.