colour off lining

[deano]

i have recently reslabbed around my pool and when doing so some sand and cement fell in the pool i cleaned it out but when i took the cover some weeks later there was a black mark at the water level and when we rubbed it the colour came off the liner at this point. the pool man came and came and tested the water and said there was too much stabiliser in the pool and no chlorine was being relesed we have removed the tablets added chlorine and corrected ph as this was low. any ideas