Expert Verified Updated: March 2026

Langelier Saturation Index (LSI) Calculator

Calculate the LSI to determine if your pool water is corrosive, balanced, or scale-forming.

Quick Conclusion
The Langelier Saturation Index (LSI) is the only true way to know if your water is healthy. A score between -0.3 and +0.3 ensures your pool is neither scaling nor corrosive.

Technical Comparison

LSI ValueWater StatusAction
< -0.3CorrosiveAdd Calcium/Base
-0.3 to +0.3BalancedMaintain
> +0.3ScalingAdd Acid

Actionable Steps

Pro-Tip

The 'TFP' method focuses on FC/CYA ratio, but the LSI is the ultimate judge of whether your water is literally 'eating' your pool surface.

Frequently Asked Questions

What is balanced?

0.00 is perfectly balanced, but anything within 0.3 offset is acceptable.

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