I have one of the cheap ferry-morse testers... I used it when I made the mix I use in my pots. From my time running my marine aquarium, I happen to know the PH of my water is VERY alkaline (~8.2 iirc), the soil in my garden is quite alkaline as well due to the Lime beds that were dredged up and used to fill the swamp that my property used to be... I use a lot of Black Cow, and Peat Moss to bring it down...
I've never augmented the PH of the water that I use to water my plants with... But I do notice a significant difference between tap water, and rain water. I have a mild kelp based fert/foliar spray that has a very acidic PH, I might try to use it to balance the PH a bit when I water (not much right now, since its raining alot).
I hear h2o2 will help adjust your PH as well, but that seems controversial. I'm going to do some experiments on two sacrificial plants. *evil chuckle*
My tap water is also well buffered... Just using a PH down additive for the aquarium didn't work, I had to find one that would bring it down, and had stabilizers in it, else within a week, without adding any extra water, it would bounce right back up.