Two case studies are presented in which a continuous loss of capacity in two samples of acid resin, are observed over 900 cycles of loading and regeneration. By completing the batch kinetic testing of the resin at different turbulences and calculating the intra-particle diffusion rates of the counter and co-ion, the effect of turbulence on the independence/dependence of the intra-particle diffusion could be established. A systematic loss in capacity and change in kinetics is reported in both case studies and it is postulated that the reason for this is the loss of active sites within the resin matrix. The significance of this observation is that standard tests done for a new resin application could significantly overestimate the commercial performance of the resin concerned. This paper proposes a method in which resin might be studied prior to inclusion in a particular process, with the objective of determining its effective life span. (C) 2009 Published by Elsevier Ltd.