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In the high-surface-potential Schulze-Hardy rule, the critical coagulation concentration scales approximately as $z^{-6}$ with the counterion valence. HenceThe more highly charged counterion therefore requires about eleven times less concentration in this idealized estimate. This assumes the cations are the counterions of a negatively charged surface, the surface-potential regime is appropriate, and the only changing mechanism is electrostatic stabilization. Specific adsorption and hydrolysis of aluminium ions can invalidate this scaling; matching ionic strengths instead is not the same prediction.

In the usual high-surface-potential Schulze-Hardy rule approximation, $c_{\mathrm{ccc}}\propto z^{-6}$, where $z$ is the magnitude of the counterion valence. Consequently,Multivalent counterions screen surface charge much more effectively and strongly lower the electrostatic barrier. The sixth-power estimate includes the way the critical ionic strength and screening condition change with valence; merely scaling the ordinary Debye length at fixed salt concentration would not derive it. Specific adsorption, charge regulation or ion correlations can produce substantial deviations.^[ref]