Thanks for all the help. We have the pH up to 7.4 now, with a daily dose of borax added with a dixie cup.

Since we only have another 3 to 4 weeks of swimming season left here (partial shade and no heater) before we drain and store the pool, hopefully we'll now manage to keep the pH stable without any large changes. I've gotta say the SWG is a technological miracle -- it's kept our chlorine level sufficient and the pool water crystal clear all season without a lot of effort.