Both carbonates can do it. Potassium in quantity will produce a bitter flavor AKA light salt. Calcium is slow to react so you don’t see instant results.
For the purpose of flavor what you actually want is to decrease the titratable acidity. If I had northern grape juice I would chill it to form potassium bitartrate. ,,, NOT actually try to raise the pH. If I had a southern juice I would check the TA, if above 0.7% TA I might pull acid out. Again might, since we deal with acid every year.
For shelf life I would aim for a pH slightly under 3.5. I know that with a year of age the wine will taste sweeter, and low pH gives better chemistry. (A contrast cola soda comes in at pH 2) ,,,, Flavor is TA. High pH gives bad shelf life.