I was gifted half a dozen healthy, gorgeous white crested black Polish hatchlings this past Wednesday. They all seemed to be so healthy and doing SO well. Well, between yesterday and today, 3 have just gotten weak, laid down, and died. A 4th is starting to exhibit some of the same symptoms. They did have trouble understanding the concept of the nipple waterer the first day, but after the first chick died in case dehydration was the problem, I put a dish of water in the brooder with them in case she died from lack of water. They started drinking from that and seemed ok. Within a few hours of the first one dying, though, a second died, then this morning, a third one. Do they need chick grit at this stage? I tend to prefer to let my broodies raise the chicks because they seem to have fewer health issues when the broodies do all the work. But my broodies have their own chicks right now. Of note, I have two feed store chicks in the same brooder with these guys & they are only about 5 days older than the Polish chicks. They have zero symptoms. What could be causing this?