I HAVE A 18 X 36 INGROUND POOL WITH A WHITE CEMENT COPING THAT FINISHES IT OFF. THE PROBLEM IS WHEN I REMOVE THE SOLID LINER FROM BEING INPLACE ALL WINTER, I NOTICE CONSIDERABLE AREAS OF DISCOLOR OR STAINS ON THE WHITE COPING. HOUSEHOLD DETERGENTS DON'T WORK TO MY SATISFACTION AND I AM LOOKING FOR SOMETHING STRONGER. CAN YOU HELP?