Free LSI Calculator for Pool Pros
Calculate the Langelier Saturation Index instantly. Enter your pool readings and get immediate recommendations for balanced water chemistry.
Ideal: 7.2 - 7.8
Ideal: 200 - 400 ppm
Ideal: 80 - 120 ppm
Ideal: 30 - 50 ppm
Langelier Saturation Index
-0.44
Corrosive
Water is corrosive and may damage pool surfaces and equipment. Consider raising pH, calcium hardness, or alkalinity.
Understanding the Langelier Saturation Index
The Langelier Saturation Index (LSI) is a crucial measurement for pool professionals. Developed by Dr. Wilfred Langelier in 1936, this index predicts the tendency of water to deposit or dissolve calcium carbonate.
The LSI Formula
LSI = pH + TF + CF + AF - 12.1- pH: Actual pH reading of the water
- TF: Temperature Factor (based on water temperature)
- CF: Calcium Factor (logarithm of calcium hardness)
- AF: Alkalinity Factor (logarithm of total alkalinity)
Interpreting LSI Results
Water is properly balanced. Ideal range for pool surfaces and equipment.
Water will etch plaster, corrode metals, and damage equipment.
Water will deposit calcium scale on surfaces and cloud the water.
Frequently Asked Questions
What is the Langelier Saturation Index (LSI)?
The LSI is a calculation that predicts whether pool water will deposit calcium carbonate scale or corrode metal surfaces. A balanced LSI is between -0.3 and +0.3.
What does a negative LSI mean?
A negative LSI indicates corrosive water that can damage metal equipment, plaster, and concrete surfaces. To raise the LSI, you can increase pH, calcium hardness, or total alkalinity.
What does a positive LSI mean?
A positive LSI indicates scale-forming water that can deposit calcium carbonate on pool surfaces and equipment. To lower the LSI, you can decrease pH or dilute the water with fresh water.
How often should I check LSI?
Professional pool operators should check LSI at every service visit. Water chemistry changes with temperature, evaporation, and chemical additions.
Why does temperature affect LSI?
Warmer water holds less dissolved calcium carbonate, making it more likely to deposit scale. This is why pools can have scaling issues in summer even with the same chemical readings as winter.
Track LSI Automatically on Every Stop
PoolOps calculates LSI instantly when you enter readings, saves history for every customer, and sends professional reports automatically.
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