So as to be expected my conductivity probe was all over the place for the first couple weeks. When it became stable and I could "calibrate" it with tank water it only fluctuated 0.2-0.3ppt max, which is good for me. I then did a calibration with the 53,000 solution. I soaked the bag in my sump for 30 minutes. Rinsed my probe in RODI and used canned air briefly to blow it off. Did calibration in Advanced mode. Cut the corner off the solution bag and tried my best to make sure no air bubbles in probe (swish, gently tap probe). Clipped bag and probe into sump for 30 minutes to stabilize reading. Immediately after calibration my probe read around 32.5ppt while still in the calibration solution. This seems odd to me because if I just told it was in a 35ppt solution for calibration I would expect it to read 35ppt immediately after calibration in the same solution at the exact same temperature with nothing moving. After moving the probe to my tank water it reads 32ppt and has been very stable for a day. My tank is about 34ppt per my good refractometer which I checked in a 20c metrology lab and compared to my home environment with the same solution. I have not yet dead on verified the 2 apex probes I have in my sump so I am taking my decent calibrated digital thermometer and will have it put into a probe calibration well at 78F to get an accurate offset from the calibrated accuracy of +/- 1deg so I should be able to set my apex probes with a little less measurement uncertainty (this is probably overkill). Oh and my TC is default 2.2.
So all that said, I am going to try again with a new bag soon. Any ideas on where the problem might be?
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