My speckled sussex chicks are 7 weeks old. One chicken at a time seems to have dark green/black diarrhea for the last 4-5 weeks. There has never been any frank blood visible in it. They seem healthy enough other than that...eating, drinking and running around. Theyʻve been on medicated chick crumbles since I got them at 2 days of age. Last week the feed store recommended Sulmet. So I put it in their water for 3 days. Didnʻt seem to make much of a difference. Then for 2 days all looked good---normal poop. Today again the dark green diarrhea came back again. Theyʻve been out in the chicken ark for a week now. Any suggestions? Do I need to pay to have a stool specimen analyzed by the vet? I am very new to this. Please help.