I'm certainly not an expert on water treatment. As I said, I am fortunate with my water, and in my case the gypsum and CaCl works fine. If my pH meter is to be believed (and that is a big if), my mash pH for a bitter comes in very close to 5.4, but the alkalinity of my water is about 42. Based on what I have read, I'm not so sure that I would like to add extra Na with the high SO4 levels. My Na comes in close to 8.5 ppm, and I find that acceptable. Perhaps you could use chalk instead of baking soda, but I have no idea how much you would need to add.