Hello I have gone through your question and understand your concern. Passing of black stool suggest gastrointestinal bleeding and to be specific from upper gastro-intestinal pathology. Any internal bleeding in upper gastric tract will alter in color due to action of enzymes leading to black or tarry stool. Eating food that is black in color like blue or blackberries, ingestion of charred food may also be the cause. Gastritis may also be cause of bleeding caused by bacteria, virus or protozoa. Undergo a test for occult blood in stool and consult a doctor. dehydration have to be prevented by intake of oral rehydration salts for loose stools.Hope your concern is answered. Thank you.