I have several groups of chickens in small coops so it is pretty easy for me. I take each chicken out and put them in a cage and wait till the poop at least twice. If both are runny or a very loose consistency, I know that is the one who is having a problem. I repeat with everyone in the group and treat the ones who are affected. Every chicken will have a cecal cleansing poop one to two times a day. Those are different in consistency and color. That is why you want to leave them through at least two samples. You can take the sample of the non cecal dropping to a vet and they can run a fecal float test for worms or cocci. You can then treat accordingly.