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What is LSI (The Langelier Saturation Index)?

What is LSI (The Langelier Saturation Index)?

The LSI is basically a way to determine if water is corrosive (negative LSI) or scale-forming (positive LSI). LSI between -0.30 and +0.30 is the widely accepted range, while 0.00 is perfect equilibrium. 

There are five variables you need to test for calculate the LSI:

  • pH
  • Water Temperature (ºC)
  • Calcium Hardness (ppm)
  • Total Alkalinity (ppm)
  • Total Dissolved Solids or TDS (ppm)
If LSI Index is between -0.3 and +0.3 pool water is Balanced, If LSI index is between -1.0 and +1.0 it is mildly out of balance. And If LSI index is between -3.0 and +3.0 water is severely out of balance and should be immediately corrected.
The closer your water is to 0, the less it will cost you to fix any problems, so checking your LSI index periodically (once a week) is recommended.

When pool water is balanced, it has no effect on the pool or equipment. There are two values you can readily change to help improve your LSI value to get it into the optimum range: pH and Alkalinity level.

If LSI Index is less than -0.3 pool water is Corrosive.
Pool water may cause etching, pitting, dissolving and staining of walls, grouting and plumbing.

If LSI Index is greater than +0.3 pool water is Scale Forming.
Pool water may deposit excess minerals on the pool and equipment. Scale generally appears as white or lightly colored rough blotches on the pool walls. It also adheres to other objects in the pool, piping and filter system. Scale can restrict water flow, shortening filter runs and reducing filtration efficiency.

In order to make sure your water is balanced and thus avoiding unnecessary equipment repair or replacement, we recommend you periodically (once a week or more) test your water balance. The easiest way to do it, is to use one of our pro kits, get the 5 results fed into our eXact iDip app and the LSI index will be automatically calculated (no math required).

Option 1:

• Pool eXact® EZ Professional Kit (486201-K2)

Option 2:

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