What is the Langelier Saturation Index (LSI)? | Orenda Whiteboard
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- เผยแพร่เมื่อ 9 ก.พ. 2025
- Understanding the Langelier Saturation Index (LSI)
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The Langelier Saturation Index (LSI) is a formula developed from studies conducted by Dr. Wilfred Langelier in the early 20th century. The LSI is the basis for water balance, and measures the relative saturation of calcium carbonate (CaCO3) in water. Under-saturation (low LSI below -0.30) means water is aggressive, and seeks calcium to reestablish equilibrium. Over-saturation (high LSI above +0.30) means water has too much calcium and it can no longer hold it all in solution, so it deposits some out in the form of carbonate scale: blog.orendatec...
We at Orenda prioritize LSI first, then Range Chemistry (with the exception of pH). blog.orendatec...
The LSI Equation
(pH) + (Temperature ºF) + (Calcium Hardness) + [(Total Alkalinity) - (CYA correction factor @ current pH)] - (TDS factor) = LSI
LSI measures water balance and equilibrium.
Ideal saturation of CaCO3 is 0.00 LSI. Under-saturation is corrosive, and over-saturation is scale-forming. Balanced water, however, is happy, and will neither etch, nor scale. Obviously our objective at Orenda is to be proactive, and maintain LSI Balance and manage calcium: blog.orendatec...
There are six variables you need to calculate the Langelier Saturation Index:
pH
Water Temperature (ºF)
Calcium Hardness (ppm)
Alkalinity (ppm)
Cyanuric Acid/Stabilizer (If applicable, correction based on pH)
Total Dissolved Solids (ppm)
More about the LSI factors
pH: this variable is the most likely to shift up and down, as pool operators already know. In the LSI calculation, it has no factor, just the pH value itself (example: 7.2). The lower the pH, the more acidic, and the higher the pH, the more alkaline.
Calcium on salt cell, scale
Salt cells generate heat, which encourages calcium to fall out of solution and form scale. Temperature (ºF): Temperature affects the speed of chemical reactions in water. This explains why salt cells often have calcium carbonate scale on them (heat).
Calcium Hardness: This is a measurement of how much calcium is dissolved in the water. Water that is over-saturated with calcium is likely to be more scale forming, but only if the pH and total alkalinity allow for it to come out of solution. Calcium hardness-like total alkalinity-serves as a buffer for pH.
Alkalinity: In the original Langelier Saturation Index formula, Dr. Langelier used total alkalinity. Over time, however, it became evident that swimming pool chemistry is different from other types of water; therefore it is more accurate to use carbonate alkalinity.
Cyanuric Acid (stabilizer): If CYA is present, adjust total alkalinity with the cyanurate correction factor in the chart above to find the carbonate alkalinity.
Total Dissolved Solids (TDS): TDS is a measurement of everything that is dissolved in the water, floating around in suspension.
The LSI offers a different way of looking at water chemistry. By understanding how saturated the water is with calcium, it is a strong predictor of damage to gunite/plaster before it gets bad.
Manage your LSI with the free ORENDA App, available in iTunes and GooglePlay.
Eric has such a hypnotic speaking voice, he could be discussing any topic under the sun and still have my undivided attention.
Thank you, that's why we hired the guy. But your secret is safe with us.
Orenda (Eric)... Thank you for making such a difference in the swimming pool community. Lack of knowledge or ignorance of facts is rampant in this industry. I appreciate everything you do and the tools you provide to us.
We try! Thank you.
Looking for cooling tower LSI explanation but you did a great job. Short and sweet! Thanks
Thank you. The LSI is the same for cooling towers, minus the cyanuric acid. You can still use the Orenda app for those calculations, but the temperature limit on the app is 104ºF, so a cooling tower's temperature is likely to be much higher.
Love this video, pass it along all the time
Thank you
Well explain... Can you explain RSI and PSI....
RSI is the Ryznar index, which is more for corrosion of metals, but it is similar to the LSI. Not sure what the PSI is... pounds-per-square-inch?
What about MSI and KSI
@@mz7289what about FBI and CIA 😉
What if the temp is 67 degrees and its not on the index. How do I determine the temp to pug into formula?
Use the Orenda Calculator in the Orenda app. Every single degree is factored in
There have been many issues here in Australia with fiberglass pools having damaged/ chalking / faded gel coats (waterline and shell under pool loses it's glossy look etc)
If the pool was drained, the shell would look very white compared to it's original color.
Do you think this is an LSI issue?
It has clearly happened at times from over chlorination and is what pool builders refer to as chlorine bleaching etc (passing blame back to maintenance businesses for the damage to surface)
I have personally looked after multiple pools from initial construction and kept water chemistry very balanced and some of these pools are showing damage to gel coats in just 2-3 years.
What's your ideas on it?
Love the vids you guys make.
Yes, in fact we’ve been looking into this and will publish an article and video about it eventually. Our understanding is the gel coat becomes weakened by aggressive water, and eventually chlorine can oxidize some of the components in it, turning those components of the gel coat white.
In your case there’s a good chance it’s happening if/when the water is cold and the LSI is not being maintained, though the rest of water chemistry might be. We see this often. Contact us at podcast@orendatech.com for more specific info.
Awesome, thank you! (subscribed)
Thank YOU!
Question : if in Shrimp seawater Aquaculture is it possible to have low LSI so it draw calcium from the shrimp exoskeleton ? eventually killing or weaker the molting shrimp ?
Hmmm... that's a great question and we are not at all experts or qualified to answer it. Perhaps in theory? But we honestly don't know.