pH control is recognized as a challenging and industrially important problem due to its highly nonlinear and time-varying characteristics. In the literature it is well known that the traditional PID controller gives a poor performance in controlling pH processes. This article studies the practical implementation problems of a commercial PID controller with gap action for the control of pH. Design principles and tuning procedures are proposed first by introducing the gap action to incorporating the high nonlinearity of the pH processes. Then the parameter tuning curve of the gap action is developed over a large operating range of pH. Therefore, the typical minimum error integral tuning formulas can be directly used to set the suitable PID controller parameters. Simulation results demonstrate satisfactory performance of the proposed pH control strategy.