What is Swimming Pool Calcium Hardness?

Author : xiaowei wei | Published On : 04 Jul 2024

What is Swimming Pool Calcium Hardness?

Calcium hardness is a crucial aspect of swimming pool maintenance that ensures the longevity and safety of your pool. It refers to the amount of dissolved calcium in your pool water, which directly affects water quality and the lifespan of your pool surfaces and equipment. Understanding and managing calcium hardness is essential to prevent problems such as scaling, cloudy water, and corrosion. In this blog, we’ll discuss the causes of high calcium levels, the ideal calcium hardness range, and methods to lower calcium hardness in your swimming pool.

Causes of High Calcium Levels

High calcium levels in your pool can be attributed to several factors:

1.Source Water

The water you use to fill your pool can significantly impact calcium hardness. In many areas, tap water or well water has high levels of calcium, known as "hard water." When you fill your pool with hard water, you are already starting with elevated calcium levels. Regularly testing your source water before adding it to your pool can help you manage calcium levels more effectively. If you live in an area with hard water, you might need to use a water softener to treat the water before it enters your pool.

2.Chemical Additives

Certain pool chemicals, especially those used for sanitization like calcium hypochlorite, can increase calcium levels over time. It’s important to choose your pool chemicals carefully and be aware of their effects on calcium hardness. For instance, using non-calcium-based chlorines like sodium hypochlorite or lithium hypochlorite can help maintain balanced calcium levels. Additionally, some pH adjusters and algaecides contain calcium compounds, contributing to the hardness.


Water evaporation is another common cause of increased calcium hardness. As water evaporates, it leaves behind calcium and other minerals, leading to higher concentrations. This is particularly prevalent in hot climates or during peak summer months. Regularly topping off your pool with fresh water and monitoring evaporation can help mitigate this issue. Using a pool cover can significantly reduce evaporation and the associated concentration of calcium.

Ideal Calcium Levels

Maintaining the correct calcium hardness is vital for the health of your pool. The ideal range for calcium hardness is between 200 and 400 parts per million (ppm). Staying within this range ensures that your pool water is neither too corrosive nor too scaling.

Consequences of Imbalance

Low Calcium Levels: When calcium hardness is too low, the water becomes corrosive. This can damage pool surfaces, plumbing, and equipment, leading to costly repairs. Corrosive water can etch concrete, plaster, and grout, and also corrode metal fixtures and heating elements.

High Calcium Levels: Conversely, high calcium levels cause scaling on pool surfaces, waterline tiles, and equipment. This not only looks unsightly but can also impair the function of your pool’s filtration system and cause cloudy water. Scale build-up can clog pipes and reduce the efficiency of heaters and pumps, leading to increased energy consumption and maintenance costs.

How to Lower Swimming Pool Calcium Hardness

If your pool water tests show high calcium hardness, there are several steps you can take to lower it:

1.Partial Draining and Refilling

One of the most effective methods to reduce calcium hardness is to partially drain your pool and refill it with fresh water. This dilutes the calcium concentration. It's essential to follow safety guidelines when draining your pool to avoid structural damage. Generally, replacing 20-30% of the pool water is sufficient for significant improvement. Ensure the water you refill with has lower calcium levels to achieve the desired dilution.

2.Chemical Treatments

Using sequestrants is another way to manage high calcium levels. Sequestrants bind with calcium ions, preventing them from forming scales. These products are added to the pool water and work by keeping the calcium in a soluble form that does not precipitate out. Sequestrants need to be added regularly as part of your pool maintenance routine, as they break down over time and with exposure to sunlight.


There are also specialized chemicals designed to lower calcium hardness. These products, often referred to as "hardness reducers" or "calcium reducers," can be added directly to the pool water. Always follow the manufacturer’s instructions for dosage and application.

3.Preventative Measures

To prevent future increases in calcium hardness, consider the following tips:

Use Pool Covers: Pool covers help reduce evaporation, which in turn prevents the concentration of calcium and other minerals.

Regular Testing and Maintenance: Frequently testing your pool water and performing routine maintenance helps catch imbalances early. Adjusting chemicals as needed keeps your pool water within the ideal range.

Source Water Treatment: If your source water is naturally high in calcium, consider installing a water softener to treat the water before it enters your pool. This can significantly reduce the amount of calcium introduced into your pool.


Maintaining proper calcium hardness is crucial for the longevity and enjoyment of your swimming pool. By understanding the causes of high calcium levels, knowing the ideal range, and implementing methods to lower calcium hardness, you can ensure your pool remains a safe and pleasant environment for swimmers. Regular testing and proactive maintenance are key to achieving balanced pool water. Enjoy your crystal-clear pool all season long by keeping an eye on calcium hardness and taking action as needed.