Acidity levels affect water chemistry and the Chemical Reaction Networks (CRN) encountered within it. In other words, pH is an external factor that influences speciation, precluding or promoting the appearance of certain chemical species as shown by distribution diagrams. Therefore, there is not a unique CRN for the entire pH spectrum. Moreover, it might be the case that an operative CRN for a given pH interval also supports the steady states values engendered by a second CRN which is operative for a distinct pH interval. In this sense, the first CRN is steady state equivalent with respect to the second CRN. Due to their importance for pH regulation in water chemistry and similarity in their speciation diagrams, we consider the well-known phosphoric acid-calcium carbonate system as a case study to show how steady state equivalence allows us to find relationships between reactions in speciation. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.