There is no reason to maintain a specific pH in a planted tank. CO2 cannot drop the pH too low for the plants or fish, even if the KH is 2 dKH.* But, when you add baking soda to increase the KH, you are messing with the fish's osmotic balance, and that may not be good for them. If you want to use a pH controller, first set the bubble rate so a drop checker tells you you are near the optimum 30-40 ppm of CO2 in the water, then slowly, a little bit each day, increase the bubble rate, until the plants pearl a couple of hours or so after the lights come on, but the fish don't head for the surface and "gasp for air". Now, set the pH controller to control the pH to whatever it is at that bubble rate.
Unfortunately, the bubble rate for optimum CO2 varies depending on how much plant mass you allow to build up, how severely you prune the plants, and how much surface water ripple you maintain. So, in the end, you almost have to tinker with the bubble rate often, to keep the CO2 concentration at the optimum level.
If you drop the light intensity down to moderate to high, instead of high intensity, maintaining the bubble rate at the optimum point isn't nearly as necessary. That lets you enjoy the fish and plants more, and prune and adjust the bubble rate less.
*The reason that CO2 won't drop the pH too low is associated with the solubility of CO2 in water, the mix of carbonic acid, carbonates and dissolved CO2, as the pH drops, as I recall. It has been several months since I picked this up from The Barr Report, and did the calculations to determine the lowest pH that CO2 can drive aquarium water to, so I don't remember the details now.