Ezil and Ray, thanks for the comments. With so many variables I'm thinking I should get some test strips. Any ideas on reliable strips for a good price?
The Hydrion papers are quite good. I carry them, but if you go to a pet store, aquarium pH papers are fine, too, as long as you get them with a broad enough range.
The reason I say that is that, let's say your papers measure from 5 to 9, and your true pH is 3, the test strip will indicate 5, as that's as low as it can go.
I used to use the strips or test kits for aquarium water, but found them unreliable for all the reasons Ray mentioned. I bought a TDS and a pH meter and have them regularly calibrated. I find that to be more reliable. It was worth the investment for me.