Our chlorine pool brick (or is it concrete) bullnose coping started staining 8 months after construction. White and grey stains at the bottom of the rounded edge. Overhang is 1". The coping is wet in the morning, even when no activity ( no rain, no splashing). It takes days to dry. All sides of pool impacted. Builder had coping cleaned using pumice stone. No change. Any advice on next steps with pool company as this is a warranty item?