Liner stain

I recently had the concrete around my pool sanded and painted.  The workmen also sanded and spray painted the aluminum coping around the pool.  After they vacuumed out the debris from the pool, the entire liner had a splotchy brown stain on it.  The stain responded to Vitamin C and I succesfully treated it with Ascorbic acid.  Is it possible that the aluminum dust from the coping caused this staining?  I had just shocked the pool the day before they started work and the pH and alkalinity were good.

It sounds like the metal they sanded off got into the pool and caused your stain. The high chlorine level could have helped expedite the metal staining. I would add some metal control to the water so that you don’t have any future staining.