I have a pebble finish plaster pool that had some steel furniture blow into the pool. The furniture was not rescued from the pool in a timely fashion and thus left a few rust stains about the size of a quarter. I was wondering what was recommended to remove the stains. I've heard of using vitamin C tablets, PH Down, Muriatic Acid, and so forth. The stains are about 6 feet under water and I would like to try something without having to drain any water.