I have a question/thought for you. Have you tried putting colloidal silver in their water? It works wonderfully well on humans I am sure it would work wonders on chickens. Depending on the strength of the silver a few drops per gallon for about a week would be enough to see a difference.
I was also wondering if the runny poop was coming from the relatively healthy chickens who have had antibiotic shots. If so give them some acidophilus. This is a naturally found organism in stomachs to help process food. Antibiotics will kill it off and cause runny poop. Once it is replaced things will return to normal. (by the way if you don't want to buy just acidophilus you can give them plain yogurt... it is added to many yogurts now. Just read the ingredients)
Keep us posted with updates.
I was also wondering if the runny poop was coming from the relatively healthy chickens who have had antibiotic shots. If so give them some acidophilus. This is a naturally found organism in stomachs to help process food. Antibiotics will kill it off and cause runny poop. Once it is replaced things will return to normal. (by the way if you don't want to buy just acidophilus you can give them plain yogurt... it is added to many yogurts now. Just read the ingredients)
Keep us posted with updates.