Oh no, I'm sorry you're dealing with the dreaded cocci. I’m glad you started treatment asap and hope your chickens will be ok. Cocci can be devastating. I dealt with a few outbreaks last year and was lucky I only lost one bird. I was feeding (amprol) medicated feed too.
You know what's funny though. Lily raised her last year babies in the same area/pen next door and NONE of those chicks got sick. Kind of makes me go hmm. I was reading a blog with some interesting thoughts about the subject. To quote:
"In addition to feeding non-medicated feed, while the chicks were still in the brooder, i started giving them small amounts of the soil that my flock regularly poops in - in their brooder, so they could scratch through it and get exposed asap. Also, on the very first sunny warm day, i put them all on the ground in the run and let them "free range." Then, as soon as they were feathered in - and as long as it hasn't been raining - i started letting them run the run all day every day. They've been doing that virtually every day for about a month [about six weeks at the date of this chicken chat post], and i have - for the first time ever - had no outbreak of coccidiosis.
I'm no scientist, but i think a lot of people are going about this all wrong. From what i've read, the way to protect a chick from being overwhelmed by cocci protozoa is by exposing them ASAP, just like a mama hen does.
Keeping their environment perfectly spotless and keeping them from being exposed to chicken poop - even though it seems to be the right thing to do - is what seems to be making them more vulnerable in the long run."
Just some food for thought, please don't take that literal. Oh, and after treating for cocci, I like to feed a probiotic like plain yogurt (just sprinkle crumbles on top to get them eating if they seem unsure) or ACV in their water once a week. I really believe it helps to repair gut bacteria and maintain a healthy system.