If you use pressurized CO2 and shut it off at night, the PH will go up as much as one unit by morning. Many of us do that, with no problems. So, I doubt the need to go slowly with raising KH/PH. I do it every water change, and do it by dumping in dissolved baking soda. I probably wouldn't try to raise KH by more than a couple of degrees at a time, but that is hardly going slowly.