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CALCITE SATURATION INDEX (CSI) AND WHY IT IS NECESSARY TO CALCULATE THIS FOR SWIMMING POOLS

The calcite saturation index is a calculation tool for estimating the likelihood of plaster corrosion or calcite scaling due to water elements present in your pool or spa. The Langelier Saturation Index (LSI), is a very similar but slightly less accurate measurement tool. The CSI uses pH, total alkalinity, chlorine, cyanuric acid, temperature, borate, and salt levels to estimate the likelihood of problems. A low calcite saturation index means the water is likely to dissolve calcite out of plaster, pebble, tile, stone, and concrete surfaces (and perhaps fiberglass) in and around your pool which will eventually cause damage when the calcite reaches levels which deteriorate the gunite or deteriorate pebble, stone and rock. A high saturation index means the water is likely to deposit calcite scale on the walls of the pool and in create scaling problems in the pool or spa’s plumbing.

If you own a plaster pool, it is best to try and get your CSI a little below zero, so that changes in pH won't shift your pool too far towards corrosion or scaling. If you have a vinyl pool the CSI can be kept slightly negative, which makes it very unlikely that pH changes could get the CSI into the range that causes scaling.