I have a 5 yr old gunite pool that has staining for calcium hardness. Pool was filled with deep well and from the advice of waterbear we refill from our treated water. We have a 12-13,000 gal pool with spa. Walls and bottom are gray in spots. No damage to the plaster, just ugly! We have drained most of the pool due to other work done at our home. Thought it would be a great time to clean up the ugly stains. Any advice would be greatly appreciated. We did acid wash out brick house after the construction and it turned out great. We had a soft faced bring so had to be very careful.