Table 1.

Equations and classifications of Langelier, Ryznar and Pockorius indexes [2], [3], [4].

Index	Equation	Description	Value	Water condition
Langelier	LSI = pH-pHs	LSI = Langelier Saturation Index	LSI > 0	Tend to precipitate
LSI		pH = pH measured in situ.
		pHs = pH at saturation
		pHs = 9.3 + A + B - C - D	LSI = 0	Equilibrium
		$A=\frac{(\log 10\mathrm{TDS}\mathrm{–}1)}{10}$
		B = [−13.12log10(273 °C+T)]+34.55 C = log10[${\mathrm{Ca}}^{+2}$mg/L as ${\mathrm{CaCO}}_3$]−0.4	LSI < 0	Tend to corrosion
		D = log10 [Alk. mg/L as ${\mathrm{CaCO}}_3$]
		TDS = Total Dissolved Solids mg/L
Ryznar	RSI = 2 pHs-pH	RSI = Ryznar Stability Index	RSI < 5.5	Highly scale-forming
RSI		pHs = pH at saturation
		pH = pH measured in situ	5.5 < RSI < 6.2	Relatively scale-forming
			6.2 < RSI < 6.8	Balanced
			6.8 < RSI < 8	Low corrosion
			RSI > 8	High corrosion
Puckorius	PSI = 2pHs−pHeq		PSI < 5.5	Tend to precipitate
PSI		pHs = pH at saturation	5.5<PSI<6.5	Optimal range
		pHeq = 1.456 Log(Alk) + 4.54	PSI > 6.5	Tend to corrosion