Brief Answer:
It can be due to occult blood.

Detailed Answer:
Hi

Thanks for choosing HealthcareMagic for your query.

Black stool can also be a indicator of serious condition, such as bleeding in the digestive tract caused by a peptic ulcer(as you hsve history of reflex disease). Black stool that is tarry in texture and foul smelling is often a symptom of upper gastrointestinal bleeding from the esophagus, stomach or small intestine. This is called melena.

Bleeding that takes place in the esophagus, stomach, or the first part of the small intestine most often causes the stool to appear black or tarry.

Bleeding in the upper part of the GI tract will most often cause black stools due to: Abnormal blood vessels. Bloody or tarry stools refer to a stool sample that's either dark red or black in color. Bloody or tarry stools can indicate bleeding or other injuries in your gastrointestinal tract.

You may also have dark, discolored bowel movements after eating dark-colored foods

Suggestion-
Wait for a day or two, If things are not better then few tests are to be done
Stool for occult blood.
upper g.i endoscopy
Colonoscopy to rule out the possible cause of blood.

But initially first confirm it whether stools contain blood or not(By test called stool for occult blood).

Thanks

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Brief Answer:
No its asome thing else.

Detailed Answer:
Hi again dear.
As er your query no i dont think that black tarry stools are because of pepto bismul.
Regards

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