For those stubborn bathroom stains, rust, or crystalized hard water stains and industrial clean is probably recommended. If you don’t want to hire our professionals and want to “do it yourself”, then we recommend a product called ZAP, Cleaner and Restorer. Its intense so don’t breathe in the fumes. Wear a mask and gloves. Dilute is a spray bottle and run water after application for up to 10 minutes, rinsing thoroughly.