To raise...Lime would be better since the plants like the calcium, and baking soda is a sodium compound. But as you said, the solubility issue is important. And I have never seen lime go into solution the way I would l.ike to. Liquid up/down is best of all.

To lower... cider vinegar in your watering solution, adjust your fert water to where you want it, 6.5 if your soil pH is way too high, up to 7 if your soil is too acidic.