If you are taking multivitamins or iron supplements or iron rich food you can still have black stools
If you have any upper GI bleed then also you can have black color stool, but the hard stools could be the side effect of any medicine if you are taking or it just simply due to low water intake.
Next Steps
If you persistently having black stools, its better to check your hemoglobin level to rule out any GI bleed, if it is normal you dont need to worry, if any abnormal findings in CBP kindly consult with gastroenterologist for further evaluation treatment and management.
Health Tips
Please increase your fluid intake and avoid eating fast food or junk food or too much deep fried food