Calcium Hardness: Managing Your Pool and spa’s Key Element

The two parameters of water quality namely calcium hardness and pH are not interrelated to each other. The following is the effect of calcium hardness on pH in your pool water:

1. **Water stability and calcium hardness**: Calcium hardness is defined as the concentration of calcium ions in water. If calcium hardness is too low, the water is “soft” and can leach calcium from pool surfaces, thus causing erosion and damage to the plaster or grout. When it’s too high, the water is “hard” and can cause scale buildup, cloudiness, and stains.

2. **pH, Alkalinity, and calcium hardness interrelation**: A combination of high pH, high total alkalinity, and high calcium hardness increases the possibility of scale formation. Scale forms because calcium ions (Ca²?) combine with carbonate ions (CO?²?) present in water to form calcium carbonate, a solid deposit. This reaction is more likely to occur when pH is above 7.8, which increases the concentration of carbonate ions in water. This means that when pH levels are high and calcium hardness is also high, scaling is likely to occur.

3. **Changing calcium hardness and pH levels independently:** This is unlike alkalinity where the pH is affected. However, pH levels can be adjusted using acids (such as muriatic acid to reduce pH) or bases (such as soda ash to increase pH), whereas calcium hardness is generally adjusted using calcium chloride (to raise) or dilution (to lower). However, if you are managing scale, you will often have to reduce both pH and calcium hardness to prevent more scale from forming.

4. **Balanced Water Index**: The Langelier Saturation Index (LSI) is used in pool care to assess the overall water balance of pH, calcium hardness, alkalinity, water temperature, and total dissolved solids (TDS). If LSI is too high (positive), it means that there is a risk of scaling, while too low (negative) means that water is corrosive. The right LSI takes into account the effects of calcium hardness on water stability and the pH of the pool.

In summary, pH and calcium hardness do not have any direct relationship but both must be maintained at the right levels to prevent scale formation or erosion that affects the quality and appearance of your pool. This paper shows that maintaining pH between 7.2 and 7.6 and calcium hardness between 200 and 400 ppm is the best way to keep the pool stable, clear, and safe.