A fast acting, high performance patio cleaning product, with four powerful active ingredients. Xtreme Natural Stone Cleaner offers the simple way to keep any stone clean often avoiding the need for pressure washing. It is important the stone remains wet throughout during 60 minute period, as the product becomes inactive once dry. Most ingrained organic matter and grime will be removed after one application, but sometimes a second application may be required to remove all black and white spot algae.