 [ Symptoms ] what treatment options are available for osteoarthritis [ Disease ] or something very serious is happening when you have a bleeding area in the stomach the hydrochloric acid will turn it jet black and this will cause tarry stools i have no idea if this is the underlying reason but it would be in your best interest to see a medical provider right away to determine if this black stool is blood or not another possibility would be pepto bismol if you were taking it