Pool Saturation Index (LSI/CSI) Calculator

Designed Zion Pools

Inputs

Water balance

Water temp

Temp unit

Calcium hardness (ppm as CaCO₃)

Total alkalinity (ppm as CaCO₃)

Cyanuric acid (CYA) (ppm)

TDS (ppm)

If unknown, use 1000 ppm (non‑salt). Salt pools are often 3000–4000 ppm.

CYA correction

Only carbonate alkalinity buffers the index.

Target CSI between -0.10 and +0.10 is a tight "sweet spot". Many accept -0.30…+0.30.

Results

Live

CSI / LSI

0.00

—

Carbonate alkalinity

0 ppm

—

Required pH for CSI 0.00

—

pHs (equilibrium pH)

—

TDS/Temp factors

—

Advisory

—

How it's calculated

Transparency

—

Formula (Langelier/Calcite Saturation Index): CSI = pH − pHs, where pHs = (9.3 + A + B) − (C + D); A = (log₁₀(TDS) − 1)/10, B = −13.12·log₁₀(TK) + 34.55 (T in Kelvin), C = log₁₀(CaH as CaCO₃) − 0.4, D = log₁₀(Alk as CaCO₃). Carbonate alkalinity ≈ total alkalinity − (CYA × correction).