Acids can etch surfaces and porcelain enamel. They help dissolve hard water deposits from shower doors, mild rust stains and soap film and remove tarnish from brass and copper.
Acids tend to bleach some stains.
Strong Acid Cleaners - Oxalic Acid . Strong Acid Cleaners - dilute hydrochloric acid, dilute sulfuric acid, muriatic acid and sodium bisulfate . These acids are used in some toilet bowl cleaners and etching compounds. They remove hard water and iron deposits and organic matter. Follow label instructions exactly.