We have 6 hens, very sweet, about 2 years old. Three Rhode Island Reds and three black Austrolorps. One of them has had diarrhea since we got them in June from some friends. They all behave and look very healthy. All are awesome egg layers. Is there anything I can add to their feed or something to help? They have been free range all summer, and are fed layer crumble. I can't even tell which one it is unless I actually see her when she poops. Any ideas what could cause and what would help? Thanks