Calcium Hardness (CH) is a measure of the concentration of dissolved calcium minerals in your pool water. While Total Hardness (TH) measures all dissolved minerals, including both calcium and magnesium,Calcium Hardness isolates just the calcium portion, which is the primary driver of scale formation and corrosion in pool water.
The Crystal Water Monitor approximates Calcium Hardness from your Total Hardness reading. We use calcium hardness to compute your Langelier Saturation Index (LSI).
The ideal range for Calcium Hardness in a swimming pool is between 150 and 400 ppm.
Low Calcium Hardness (below 150 ppm)
Water that is low in calcium is aggressive and will seek to draw calcium from wherever it can find it — most commonly your pool plaster, grout, and concrete surfaces. This leads to etching, pitting, and deterioration of pool surfaces over time. Low calcium hardness also contributes to a low LSI score, indicating corrosive water conditions overall.
High Calcium Hardness (above 400 ppm)
When calcium levels are too high, the water becomes over-saturated and prone to depositing calcium carbonate as scale. This appears as rough, white or grey buildup on pool surfaces, waterline tiles, and inside your heater and plumbing. High calcium hardness also drives your LSI higher, increasing the risk of cloudy water and reduced equipment efficiency.
Adjusting Calcium Hardness
To raise Calcium Hardness, add calcium chloride to your pool water. To lower it, the most effective approach is to partially drain and refill the pool with fresh water, diluting the calcium concentration. Unlike pH or alkalinity, calcium hardness cannot easily be reduced with a single chemical addition.