Lisa, I've had chickens for years, and I have to say that the only time I had chicks get cocci was one summer when it was ungodly hot and wet! It was the perfect breeding ground for the cocci, and my chicks that had just gone outside started having bloody droppings (but no other symptoms). I got them on the Corid in their drinking water right away, and all was well.
Just wanted to share that with you. Also, I changed the chicken run from just dirt, to sand. That has really made a huge difference. I rake the sand each day to get up all the droppings and it stays nice. Plus, you don't have mud everywhere when it rains.
Have a great day and enjoy your chicks!
Sharon