Thanks for the replies, guys. I used one of the two packs of buffer that comes with it to calibrate yesterday. It seemed to be giving me readings that were close to expected. Today, the readings I'm getting from my pool water and tap water are completely out of whack with what I think they should be, and not close to what I'm getting from the phenol red test.
As an example, my tap water is or should be around 6.8. The meter is telling me it's 7.8. I cannot account for the difference.