@MisterAeroponics is right. The plant is definitely overwatered, probably also watered with the wrong pH. This results in a nutrient lockout, which is causing your plant to show a calcium deficiency. Those are the little spots on the leaves.
However, the black discoloration looks like a fungus to me (maybe in connection with the overwatering?). If that’s confirmed, I would cut off the affected leaves as soon as possible. But I'm not 100% sure about the fungus. I would wait for more opinions on that.