I shock my pool with 3 lbs to winterize it let run through the night and their were black streaks on the bottom the next day.I tried to brush them off but it would not come off can anybody tell me what this black stuff could be.

Hard mineral stains are the most likely cause. There is a product available where pool supplies are sold that is made for mineral deposit removal. It is likely manganese, or iron.

What were the tds, ph, alkalinity, calcium hardness before treatment?

It could actually be algae spots. Did you have green algae before shocking?

What material is your pool surface?
Al