Muriatic acid is best for removing stubborn toilet bowl stains - silive.com
Remove stubborn toilet stains: How to use muriatic acid the expert way - silive.com
How to Use Muriatic Acid Safely | Hunker
Great Value Heavy Duty Toilet Bowl Cleaner | Walmart Canada
Chem Clean Limited - Chem Bowl is a very effective toilet bowl cleaner formulated with 25% Hydrochloric Acid. It quickly eliminates uric acid, iron stains, lime scale deposits, rust and foreign matter