So it turns out I did order some refractometer calibration fluid. It is about a year old but it was in a vacuum-sealed bag. Does it go off? I checked my meter and when it is set to 0 with R/O water, it reads 1.029 with the 1.026 calibration fluid. So it's about 0.003 high. I recalibrated it to 1.026 and my salinity is around 1.023 right now. I don't fully trust it so I'll keep comparing it to trusted/verified sources. But having read about refractometer errors a couple of times, this all seems somewhat reasonable although I'm still surprised it was off that much at 1.026. I am going to go forward trusting the calibration fluid over calibrating to R/O water.