Before attempting to change your soils pH, you must know its current level. This will determine how much you need to raise or lower it, if at all. A simple soil test can be done at home . You must also know your soils texture, be it clay, sand, or something in between. More material is needed to change the pH level of a clay soil than for a sandy soil because the charged surfaces of clays make them more resistant to pH changes than the uncharged surfaces of sand particles.
Generally, limestone is used to raise a pH level, and sulfur is used to lower it. Limestone is relatively pure calcium carbonate, but dolomitic limestone is a mix of calcium carbonate and magnesium. Pound for pound, dolomitic limestone neutralizes more acidity than pure limestone and adds magnesium to the soil, perfect for those who garden in the East or the Pacific Northwest where this nutrient is naturally low.
I'm glad to be hydro.