First Swim was yesterday after heating up for about 1/2 day, . Added Borates the day before and water is sparkling once again. So I have a light Travertine coping with antique white grout. In several places I have black mildew (I assume) in the grout lines. What is the best way to remove/ clean these areas. Obviously by brushing, but should I use a diluted bleach or some type of surface cleaner. I saw a pool surface cleaner by HTH @ Walmart some time ago. Whatever I use will probably end up getting into the pool, so I think I should avoid products like 409, etc. Any advice? I will most likely use this same product to clean the water line tile where the wind blew dirt to one end of the pool & collected on the water line tile.