empirical rule-of-thumb (Puckorius pHₑ𝓆): 8.47 · ionic strength 0.026 mol/L
Saturation this high will not persist. A real tower precipitates CaCO₃, consuming alkalinity and pulling pH down. Treat this as “heavily scale-forming,” not a literal concentration.
Familiar indices at tower conditions: LSI +1.75 · RSI 4.87 · PSI 4.78 · colors are untreated tendencies, a good inhibitor program routinely controls calcite SI to ~1.5 to 2
Honest framing, on the page by design: this is a screening-level saturation check built from primary thermodynamic data with Davies activity corrections, valid well past cooling-water ionic strengths. It does not model explicit ion pairs (v2 adds CaSO₄°, MgSO₄°, CaHCO₃⁺, CaCO₃° and publishes a PHREEQC agreement table). For critical decisions, rigorous ion-association modeling is the reference standard; this tool tells you when to reach for it.
Sites, systems, and saved comparisons arrive with accounts. The result stays on screen either way.
Sources & assumptions: carbonate/calcite constants Plummer & Busenberg (1982), as in USGS PHREEQC phreeqc.dat; gypsum/silica solubilities from PHREEQC databases (public domain); β-TCP Ksp from MINTEQ (25 °C, temperature uncertainty noted); activity corrections Davies (1962), valid to ~0.5 mol/L; threshold bands per common cooling-water practice, program-specific limits from your supplier take precedence; Mg-silicate row is a screening rule, pH-sensitive above ~8.5. CO₂ supersaturation factor default 6, calibrate against towers with known alkalinity, cycles, and pH before ship. The calculator estimates; the field measures.