Puckorius Scaling Index (PSI)

Refines scaling prediction by using the equilibrium pH the water tends toward after precipitation rather than the measured pH. Useful for high-alkalinity waters and cooling towers where CO2 is continuously stripped. Values below about 6 indicate scale forming, 6 to 7 balanced, above 7 dissolving.

$$\text{PSI}=2{\text{pH}}_s-{\text{pH}}_{eq}$$

Variables

Symbol	Meaning	Unit
${\text{pH}}_s$	Saturation pH at calcium carbonate equilibrium	unitless
${\text{pH}}_{eq}$	Equilibrium pH after CaCO3 precipitation and CO2 effects	unitless

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Part of The Blueprint of Water