I use powdered Corid because that is what my local TSC had, 1 teaspoon per gallon, mixed up fresh daily, if I think I have a coccidia problem. 5 days. No extra vitamins during that time. I've lost a couple chicks to cocci, and for me, it's just always been one chick out of the lot die. I had one bunch all become mildly affected -- they had ruffled feathers as their only symptom until one died with diarrhea, but I necropsied and determined it was cocci (I am a vet). That lot was already on medicated feed, but it is not a cure, only a possible preventative.....which doesn't always work.
I never give my birds dairy products. I do not think it a good idea. Best thing right now is to medicate the chicks and ensure they eat, and they won't want to eat anythng new if they don't feel good.
For the first time in months, I have no chicks in the house! Yay!