control file parameters affecting pH

I am modeling a meso-oligotrophic lake that is about 30 m in the deepest sections and it only weakly stratifies in the summer. The model is fairly well calibrated for temperature, DO and algal production (based on measured and predicted chlorophyl a data). The snapshot file shows that the pH in the upper layers is being predicted as too alkaline (ph 9-10 when measured upper layer pH is around 6.8). Which paramers in control file are best used to calibrate for pH? I am modeling 3 algal groups and applied a dark respiration rate AR of 0.03 for all three groups.