LSI vs. CSI: Understanding Water Balance

What is Water Balance?

Water balance is crucial for protecting your pool's surface and equipment from damage. Unbalanced water can be either corrosive (damaging surfaces) or scaling (leaving deposits). The LSI and CSI are two different ways to measure this balance.

Langelier Saturation Index (LSI)

The LSI is a formula that predicts the likelihood of calcium carbonate to precipitate or dissolve in water. It's been the standard in the pool industry for decades.

• A positive LSI indicates scaling conditions.
• A negative LSI indicates corrosive conditions.
• An LSI between -0.3 and +0.3 is generally considered balanced.

Calcite Saturation Index (CSI)

The CSI is a more modern and accurate index for predicting water balance, especially in pools with cyanuric acid (CYA). It's an adjustment to the LSI formula that accounts for the effect of CYA on alkalinity.

• A positive CSI indicates scaling conditions.
• A negative CSI indicates corrosive conditions.
• A CSI between -0.3 and +0.3 is generally considered balanced.

How This App Uses LSI vs. CSI

In the settings, you can choose whether you want the app to prioritize LSI or CSI when calculating chemical targets.

• CSI-First (Recommended): This is the default setting. The app will use the CSI to calculate your targets, which is generally more accurate for pools with CYA.
• LSI-First: If you choose this setting, the app will use the traditional LSI formula. This might be preferable if you are used to LSI calculations or if your pool does not use CYA.

Changing this setting will affect the recommended targets for pH, alkalinity, and calcium hardness to keep your water balanced.