I would like to suggest that chicks are cleaned more often than once a week(as stated in previous comments). How many chicks do you have 4 or more? When chicks are in crowded conditions,they are sitting,eating and sleeping in their own poop,this is a environment that cocci thrives in. I clean my brooders twice a day,morning and evening,takes only a couple a minutes,and i feel my chicks appreciate it.Hope all your chicks are feeling better.