We have a pool with a Pebble Tec "Pebble Sheen" surface. The color of the surface is "Blue Granite". I asked my wife to add some chlorine one day, and not knowing any better, she tossed the chlorine tablets directly into the pool. They settled on the bottom and left a dark, almost black stain on the Pebble Sheen where the chlorine must have had some chemical reaction with the surfacing. Does anyone have any suggestions or ideas as to how this can be repaired, either with or without draining the pool?

Thanks for any and all advice!