If you’re a pool owner and if you’ve ever gotten a professional to test your water, you’ve probably heard of this term and you just kept nodding your head pretending to know what he was talking about. While it is a pretty complex thing by itself, we’re going to simplify it and break it down to its most basic level. Ready? Here we go.
Your LSI is the overall state or balance of your water.
That’s it. Just kidding, that’s the basic gist of LSI and let’s break it down even further. The LSI or Langelier Saturation index tells you the state of your water. Water will always try to go back to its normal state. This means that if water is oversaturated (in our case, calcium) or has a high positive LSI it will do everything to can to release the excess calcium so that it will reach equilibrium, or Zero LSI. What happens then? The calcium has to go somewhere right? The effect of this is pool scales. Since the calcium is being ejected from the water molecules, they end up on your pool surfaces as scale.
On the other side of the spectrum, if your water has a negative LSI or is undersaturated, it will do everything in its power to fill in that gap and reach Zero LSI. Where does it get the calcium to fill the void? Well, since water can’t go to the shed and grab some calcium chloride, it does the next best thing, it finds the nearest source of calcium and eats it. And the nearest source of calcium? Your pool surfaces! Cement surfaces contain calcium and it’s there all around your pool water. This is the number one reason why you get corrosion on your pool surfaces.