Muriatic Acid, removes stains from concrete, no problem. Just pour some on the stain and keep away from the fumes, cause they will melt your lungs. After its not smoking so much rinse it off. This removes the stained layer of the concrete. Also great for cleaning ceramic toilets and for turning metal into rust! Dont get any on your face or skin, trust me! Also dont get any water in the acid jug. This stuff is meant to dump in swimming pools, so its okay to mix it with water, just not the other way around.