Black Marks at the Bottom of the Toilet: The Natural Trick to Eliminate Them Effortlessly.

Bonus tips
For descaling very dirty toilets, you can also rely on soda crystals (Saint Marc or any other brand)... or Coca-Cola!

Surprisingly, it works! Baking soda should be used only for regular toilet cleaning.

But used alone, it is not powerful enough to clean very dirty toilets.