Graphic poop picture...need some help please

I have 1 1/2 week old and 2 1/2 week old chicks. Tonight while letting them run around on the concrete floor, a few of them have funny poop. The first part of it is solid and the end part is brownish and getting a little runny. Is this the start of cocci? Therre are 4 different breeds and I haven't been able to catch the runny poop victims to find out who is doing it. The brooder is cleaned daily, fresh food and water and medicated feed. Any help on this is appreciated. I know I can loose them all if this is cocci and I want to be pro active and stop it if it is. Thanks ahead of time

 

Thanks so much.