What I have found with mine also running 30ml/min it takes a while for the reactor to move all the volume in the reactor to the tank even after the CO2 shuts off or goes to throttling. That can cause a bit of the overshoot IMO. I think if you are maintaining a swing of .2-.3 each day that's pretty good when you consider some of that is just up and down as pH changes from CO2 uptake in the water itself.