My Cochin bantam chicks are 2-3 weeks old. They've been doing great. Then I found my oldest chick spinning circles in my brooder. Couldn't upright herself so we put her down. Then 3 days ago I noticed 2 others starring up at the sky. Not moving as much & seem to lose balance. Then they flip over backwards & flop around! I just had 3 do this today!! They are in a big metal tank, heat light but they can get away from it. I did add Corid to their water for a week from cocci but that was 10 days ago. I do put a little ACV in the water & on chick starter from the local MFA mill.