What is it?

Scale formation is created when there is an oversaturation of minerals, particularly calcium, in the spa water and water conditions do not allow them to remain dissolved or soluble. Those conditions may be high calcium hardness, high water temperatures and/or high pH. The minerals drop out of solution and rough, sandpaper-like deposits attach to spa surfaces, circulation and filtration systems and plug heaters. Conversely, low levels of calcium make the water more aggressive and can lead to corrosion of equipment and spa surface staining.

To remove scale:

To prevent scale: