In Fig. we present the titration isotherm of colloidal particles in suspension of volume fraction 11%, containing 10 mM NaCl. using RR-cpH algorithm and the canonical-Widom reactive simulation algorithm. Furthermore, the figure also shows that the canonical simulation is in perfect agreement with the results obtained using rGCMCD method (indicated by the circles), demonstrating the consistence between two very different approaches. We must conclude that for such systems, the usual implementation of the RR-cpH algorithm is simply wrong.