P4 Calibration Problems

I noticed my Conductivity Probe was not calibrating correctly. It was reading much lower than it should have, compared to two refractometers.
It was 5 years old so I got a new one in January. The new one is not calibrating either.
I've tried both GHL and Pinpoint calibration fluid. Just calibrated again and instead of 1.0264, it's reading 1.0246 in the calibration fluid.
Any idea why this might be?
It's making me question my other probes, too like pH.

ok, now that I have the probe back in the sump, it's reading what the refractometer read... 1.028
So seems like the GHL calibration fluid I had was old/bad.
Still not sure why the fluid read low after calibration.

maybe different temp. used for compensation during calibration and actual measurement