When we burn the citronella Tiki Torches around the pool to keep the mosquitos away, it creates a sooty ring at the water line on my vinyl liner. Anyone have any good ideas on how to get rid of this? It's very stubborn and seems a little oily, as it smears.

The other day I found my wife scrubbing it with one of those blue pads. She said it was less abrasive than the green ones, but I didn't like it. At least she was using a mixture of borax and bleach instead of some detergent. (She said the borax gave it some consistency and held the bleach on the stain rather than running directly into the water.)