The invention relates to a method for maintaining an equilibrium of a physico-chemical parameter of a medium, and for recovering the equilibrium in case of loss of the latter. More precisely the method makes it possible to estimate the relevance of a corrective action on the medium in order to recover an equilibrium. The method is implemented by the processing unit of a system for regulating the medium. The invention applies in a non-limiting manner to the regulation of the equilibrium of the bathing water of a swimming pool.