Before you put down any more of them, try Corid in their water. Here is a link to the dosing info:
https://www.backyardchickens.com/t/818879/updated-corid-and-amprol-amprolium-dosing
It might be coccidiosis, which is easily treated with amprolium (Corid), which you can buy at tractor supply or most farm supply stores in the liquid or powder form. It isn't very expensive, and it might save your birds. I'd get it in their water right away.
https://www.backyardchickens.com/t/818879/updated-corid-and-amprol-amprolium-dosing
It might be coccidiosis, which is easily treated with amprolium (Corid), which you can buy at tractor supply or most farm supply stores in the liquid or powder form. It isn't very expensive, and it might save your birds. I'd get it in their water right away.