Coccidiosis is a likely culprite, but it could be other things, like a bacterial infection. When I get one that's off like that I treat it the with the Corid water, but I also give them a Corid drench, which I shoot for 20mg/kg. At 2-3 weeks old they're 100-200 grams? What I try to give mine is .02ml per 100 grams. Smaller ones get as small a drop as possible. Take the sickest one and look for discoloration on it's belly as it's possible that it has enteritis. Do you have any Baytril and can you post a poop picture?
-Kathy
-Kathy