I am new to chickens but I just got a beautiful flock of 12 hens and one Barred Rock Rooster. I also picked up three black sex linked pullets from a different farmer and put them in with the rest of the flock. On day two I noticed the sex links were sneezing and one had pooped red which I believe was lining but I don't know for sure. Two of the sex link pullets died within three day. Then I noticed the Rooster stopped crowing because he's sneezing and all congested. A few of the other hens are sneezing a bit but not to much yet. I have been treating them all for 6 days now with Duramycin -10 at a pretty high dose. The rooster does not seem to be improving, do you think there is a chance it could be Corid? I would appreciate any suggestions. Thank you.