In June, I let a broody hatch out some chicks. She turned out to be a terrible mother and the eggs were all filthy, some exploded, four hatched and she nearly crushed the chicks. She will not get to sit on eggs again. Of the four that hatched, one was deformed and had to be culled, one died when she was about 3 weeks old (she was generally not thriving). The remaining two seemed just fine. They stayed in the broader/grow out pen until almost two weeks ago when we brought back some new chickens (about 2months old to about 4 months old) to the farm. Those chickens came from an NPIP flock and looked very healthy. They were put in quarantine from my main flock, but I went ahead and tossed in our remaining two birds from the terrible hen. Keep in mind, those chicks had been kept away from our flock since the day after hatch, so for two months. A couple days ago, one of those chicks was dead. It was a chick with a vaulted skull and had been normal in the morning, so I thought that maybe his head had been hit or something. Everyone else looked fine, so I tossed some ROPA into the water just to be cautious and tucked everyone into bed. In the morning, the other of our hatched birds was standing, fluffed up and not responding. He died by 10a. The others looked fine. I added AmproMed into the water, in case we were dealing with cocci from the incoming birds' farm. The rest of the day yesterday, they all looked fine. This morning, though, one of the new birds was standing fluffed and unresponsive. Another of those birds is also looking a little lethargic and fluffy, but responsive. I put both of them in a dog crate in the garage, but I expect the worse off one to be dead soon, the other seems to be heading that way. Is it safe to assume that whatever it is came in with the new birds, or is it possible that the chicks that were hatched under the poor conditions were carrying the illness and gave it to them? I know that chicks who are hatched in places where eggs explode are prone to health issues, but I understood that to last for maybe a couple weeks, not a couple months. Does anyone have any idea what is taking out my birds? Some of them have diarrhea, and the one on the brink basically is pooping pink water. Otherwise the symptoms are just fluffing up and dying within the day. Is there anything else I can give them? All of the antibiotics I can find say to not give them to chickens who will produce eggs for human consumption, which is all of these birds except the one remaining rooster.