The Quantity of Blood Required to Produce a Tarry Stool. How much? Melena, characterized by black tarry stools, can occur with as little as 50 cc of blood in the stomach. How Types of Poop: What Doctors Need You to Know The Healthy @Reader's Digest What Your Poop Color Reveals About Your Health Let's talk about your bowels Four Seasons Dietetics Decisions: A 20 year old male with dark stool Department of Emergency Medicine Saint John Dark stool vs black stool the difference can be serious. Dark brown stool is often food or iron related. Black, tarry stool may indicate internal bleeding and needs urgent medical attention.