Sorry for your loss and thanks for posting your story. Many of us are new at this and the info on this site is really invaluable. Your story may help save someone else's chick from cocci, maybe one of mine. I haven't been able to get my 5 week chicks out on the dirt yet because their coop and run aren't done yet, so i'm worried about cocci. Reading a few stories like yours prompted me to buy Corrid, so i can treat at the first sign of illness. I've been giving them boxes of dirt that they eat and take dust baths in, but i'm not sure if that will be enough to build up their immunity.
Don't beat yourself up too much, you did the best that you could.
Don't beat yourself up too much, you did the best that you could.