If you are lucky enough to own a pool, you probably already know that keeping the chemistry of your pool water balanced is essential. The pH, alkaline content, and chlorine levels in your pool water must all be kept under control, or your pool can quickly become damaged and contaminated. 

Properly balancing your pool's water supply also means keeping its calcium hardness under control. This is especially important if you own a pool with a plaster finish, as these pools can be badly damaged by pool water with excessive or insufficient calcium hardness.

What Is Calcium Hardness In Pool Water?

All municipal water supplies contain a certain amount of dissolved calcium minerals. The amount of calcium content in your water supply will differ depending on where you live. Calcium content in water is measured in 'hardness' — water with a high calcium content is said to be hard, while soft water contains smaller amounts of calcium.

Why Is Calcium Hardness Important In Plaster Pools?

The plaster used to line swimming pools contains large amounts of calcium. If your pool water has low calcium content, an interesting but unwanted chemical reaction occurs. The water will start absorbing calcium from the pool's plaster until the plaster content in both substances reaches equilibrium.

This exchange of calcium molecules can cause etching, a process that leaves large, ugly grooves and dents on the plaster's surface. A badly etched plaster lining is much harder to clean, and the indentations on its surface will quickly accumulate ingrained dirt, algae, and bacterial growth. Etching also weakens the plaster's structural strength. In many cases, badly etched plaster will need to be completely replaced.

You might assume that adding large amounts of calcium to your pool water is an easy way to avoid this problem. Unfortunately, excessively hard water leaves calcium deposits, known as scaling, on your pool's metal and plastic fixtures. It can also make the pool water appear cloudy, and many people find their skin becomes dry and irritated after bathing in hard pool water.

How Do You Keep Calcium Hardness Under Control?

To test the calcium hardness of your pool water, you can use a standard 4-in-1 pool water testing kit. These kits are easy to use and measure your pool's calcium hardness, pH, alkaline content, and chlorine content.

If you find that calcium levels in your water are too high, you can add sequestering agents to the pool water. These chemicals bond with calcium molecules in the water, neutralizing their effects. If calcium levels are too low, you can manually add powdered calcium or water-hardening granules to your water. 

However, adding chemicals to your pool water may not be enough to keep calcium hardness levels stable. The calcium content of your water can be significantly altered by its pH, and will also be affected by sudden temperature variations. Excessive evaporation during the summer months can also cause calcium levels to spike.

Keeping all of these problems under control at once can be a complex and difficult business, leaving your plaster pool vulnerable to damaging etching. It is far safer and easier to call in a professional pool chemical balancing service. These services will carefully monitor every aspect of your pool's chemical balance and can use commercial-grade products to keep your pool's calcium hardness under control at all times.