I recently found a rust stain remover that actually works.. After trying various "guaranteed" rust removal products from Home Depot, Lowes, and garden shops, none of them ever worked. White Ox totally removed rust stains from my sprinkler system from my pool filter, shed, and pool deck. It contains Oxalic acid, which removed it within minutes. A few bad places took more than 1 treatment, but it's all gone. Just 4 little scoops in a gallon of water in a pump sprayer was all it took. Mix it up, spray it on, and rinse it off good after a few minutes. It's available at Pensacola Hardware on Gregory Street for about $30.00. The fumes are rough to breathe while spraying, but disappear in seconds. You MUST wear some good gloves and prevent getting it on your skin.. It did NOT kill any of my plants or lawn..