The saturation index (Si) relates to the calcium and alkalinity in your pool’s water – it’s an indicator of the water balance. Your water is properly balanced when the Si is 0 ±.2. If the Si is below -0.2, the water will become corrosive and can likely damage your pool’s finishes. If the Si is above +0.2, scaling and staining can occur.
Use the chart below to determine the saturation index.