I would try Corid if it were me. Here is info on coccidiosis:
http://www.clemson.edu/public/lph/ahp/disease_links/images/coccidia.pdf
Corid is in the cattle section of the feed store.
For coccidiosis I give the 9.6% solution, 9.5 ml per gallon of water as the sole drinking water for 5 days. I mix a new solution daily.
The diarrhea should subside quickly. I see improvement within 24 hours.
If it is a bacterial diarrhea the Corid won't help. You might consider some kind of antibiotic if the Corid doesn't work- I don't know.
Diarrhea isn't normal in chickens. There is a runny caecal poo that is normal- every 8th poo or so, but your situation doesn't sound normal.
I hope this helps! I won't raise baby chicks without Corid nearby- it is THAT common for them to need treatment for coccidiosis around here on our soil. They can end up with it in the brooder as well, even before touching soil, through equipment/hands.
I don't know what the diagnosis is, but if it were me I would try the Corid to see if it cures it.