I've got 19 chicks in a metal horse trough in my basement with a heat lamp on them. They are on pine shavings, are on medicated chick feed, and they've been on Avia Charge 2000 in their drinking water since hatching. Two days ago, one was sneezing occasionally, but seemed fine otherwise. Last night, I now have 5-6 of them that are all sneezing. I change their bedding twice a week. The original chick is now looking a bit lethargic (eyes half closed, sleeping more) but is drinking and eating, and I don't see any abnormal poop. I do have water soluble Terramycin, but hate to begin it for them all unless I absolutely have to, as I don't want to promote antibiotic resistant diseases. I searched here and found many folks with issues such as mine aroudn this age, but I'm not find the answer to my question, which is: how do I make a decision on whether or not to start Terramycin or something else? Should I wait it out, hoping they recover on their own, watch for unusual poop, or just go ahead and start them all on it? I do have a 6 week old chick from another hatch in with the 3 week olds - she seems fine so far, and I can remove her if necessary. Also, I was going to move these chicks to my barn pen with a heat lamp this weekend; I assume I should not do this now (they're getting crowded in the trough). Thanks in advance for your feedback and advice.