Your swimming pool’s water saturation index (also called the Langelier Saturation Index, or LSI) is a measure of how saturated your pool water is with metals and calcium. I built a pool saturation index calculator (embedded below) that you can use to figure out how saturated your pool is.
The saturation index scale goes from -1 to 1, and your pool should ideally be between -0.3 and 0.3. Why does your pool’s LSI matter?
If it’s too far in the negative, that means you are dealing with corrosion. If it’s above the ideal range, you likely have some scaling issues.
I go into a lot more depth on this topic in my separate article on pool water saturation index that you can check out if you’re interested. Here’s the calculator.
How to Calculate LSI
Intrigued to know how exactly to calculate your LSI? This is the equation:
(pH) + (temperature in Fahrenheit) + (calcium hardness) + [(total alkalinity) – (CYA correction factor at the current pH)] – (TDS) = LSI.
As you can see, as long as you know your pool’s pH, temperature (in Fahrenheit), calcium hardness, total alkalinity, CYA, and total dissolved solids levels, you should be able to calculate your LSI fairly easily with some basic arithmetic.
Check out my guide on swimming pool chemical levels to learn more about water chemistry.
Have questions about this topic or others? Drop me a line; always happy to help.