Calcium scale can build up in the pipes, jets and other components of your hot tub. It may also appear on the acrylic tub surface and as flakes in the water.

Wherever it is, calcium scale is unattractive and uncomfortable to the touch. It can also damage the working pieces of your hot tub, at the least making them less efficient.

Here we’ll discuss what calcium scale means and how you can prevent and get rid of it in your hot tub.

Calcium and Hot Tub Water Chemistry

The water chemistry of your hot tub must be properly balanced for the health and safety of users, as well as the maintenance of the tub itself.

The metrics and chemicals of hot tub water chemistry include pH, chlorine, bromine, total alkalinity and calcium hardness. When these components are out of balance you may experience corrosion, buildup and bacteria in the tub.

Calcium helps control the corrosive nature of spa water, and calcium hardness measures the level of dissolved calcium in hot tub water. The calcium hardness level recommended by the Association of Pool and Spa Professionals is 150 to 250 parts-per-million (ppm).

Calcium-low, or “soft,” water can lead to corrosion of tub components and staining of the acrylic surface. Calcium-high, or “hard,” water can allow scale to grow on the components and acrylic tub surface.

That calcium scale is what you might see as buildup on the acrylic surface, flakes in the water or clogged in the components.

The recommendation is to fill your tub with 75 percent hard water and 25 percent soft water to keep calcium hardness in the correct range. Adding or losing small amounts of water should not alter the calcium hardness in the spa.

If filling your tub with hard and soft water is not an option, be sure to add a stain and scale inhibitor (following directions on the label) to your water treatment system.

Remove Calcium Scale and Restore Proper Calcium Levels

If you find calcium scale in your hot tub, you have a few options. Your choice will depend on how much calcium scale and other buildup you have, and whether or not you want to empty and refill your tub.

Simpler options include:

• Using the stain and scale inhibitor (mentioned above).
• Adjusting the total alkalinity (explained below).

Total alkalinity measures the various alkaline substances in hot tub water. The level should be between 80 and 120 ppm in order to properly resist changes in pH level. Low total alkalinity may allow the pH level to fluctuate easily, quickly and significantly.

Ultimately, pH fluctuations can lead to calcium scaling (as well as corrosion) in the hot tub. Avoid low total alkalinity and pH fluctuations with sodium hydrogen carbonate, or Alkalinity Up.

A more complex and time-consuming way to get rid of calcium scale is to clean your entire hot tub and its components. For details, please see our article on cleaning jetted tubs.

Support healthy water chemistry and calcium hardness by keeping your filter clean and changing it every three months.

Also, never use anything sharp or highly abrasive to clean calcium scale off the acrylic hot tub surface – this could damage the hot tub permanently.

Calcium scale is unsightly, but relatively easy to prevent and address. If you have any questions, please feel free to contact your Aqua Living dealer.