My hens have white sticky crud all around their backsides, what is it?

Hi, I have a mixed flock of 8 hens, 1 rooster and 11 growing chicks on about 1 acre. I recently lost 1 beautiful sweet hen to diarrhea, so I've been watching the rest of the flock very carefully. Now, two weeks later, four more hens have developed a sticky white gunk on their tail feathers. My Eenie, who died, also had that, then it progressed to a green and water diarrhea, listlessness and no appetite. The lady at the Feed Store suggested that it might be coccidiosis and recommended sulfa, but when I read up on that the symptoms sound very different, listing a bloody stool. At this point, the infected hens are not showing the listlessness or lack of appetite, just the soiled tail feathers. They do not share food or water with the chicks, although they are together in the same hen house at night. Any suggestions?