Everything has a pH. our skin is a good example. but to measure pH you need for the solid to be in a liquid and that solid will change the pH of the liquid. Typically you would use deionised water to get the most accurate result for a pH test, and measure the effect the solid has on the pH of the deionised water.
Basically you have acids , neutral and bases / alkaline.
without going into the nitty gritty of pH and how to change it if you have basic water (high pH) and want it to go lower you need to add an acid (low pH) or something acidic like driftwood.
pH 7 is neutral.
Adding a base to basic water will not really lower the pH unless you reduce the amount of base in the solute, thereby altering the concentration of H+ and OH- ions.