What do you suggest if i have dark brown with mostly black stool this morning. should i worry?

Yes: Black stools or melena, is always considered blood. It usually comes from the stomach or the beginning parts [higher up in our jargon] of the small intestine. Bleeding from colon usually comes out red. Black been partially digested stools need to be investigated. Products containing bismouth can make our stool black, but it must always assumed to represent bleeding within the GI tract.