Biological phosphorus removal from water surfaces is an important process for the control of eutrophication. Even though much attention has been devoted to understanding the metabolism of bacteria and the effect of operational parameters on the efficiency of the phosphorus removal process, certain aspects are still unclear. The aim of this work was to evaluate the influence of pH control on the stability and efficiency of two sequenced batch reactors (SBR): one operated with pH control (pH 7.0) and the other without pH control (pH raised from around 7.8 to 8.5). The reactor operated without pH control showed higher efficiency on phosphorus removal and stability than the reactor with pH control. Based on the kinetics of both reactors it could be inferred that a different population developed in both systems.