The scale on the tile will also come off very easily with a strong muriatic acid solution and a green pad. I use a squeeze water bottle to apply the acid, wait a few seconds for it to act on the scale, and then scrub it off with a green pad. Repeat as necessary. You need to wear good eye protection and latex gloves, be mindful of the wind direction and careful of the fumes. You also need to keep it off concrete, stone, and metals.

Always remember to add acid to water and not vice versa.