Yet another question about salinity probe calibration

[VeL]

First I want to make it clear that I know how to calibrate a salinity probe and I've done it several times already. Michael's tutorial was really helpful, thanks for that :thumbsup:. However I haven't tried calibrating the probe with a 53ms @ 26.5C NSW solution, I've only used the GHL 50ms fluid. And today upon re-calibrating my probe after cleaning it, I've noticed that on the GHL fluid bottle it says "50ms at 25 C". That makes me wonder how accurate my calibration would be when my aquarium temp is 26C and the fluid is 26 C cause it floated in the sump for 24 hours. In other words the calibration fluid that is 50ms at 25C, at 26C will be something like 51.2ms but then when we calibrate we still put as conductivity value at 50ms. To me it seems that when we are calibrating we tell the Profilux "okay, our current temp is 26C, the fluid temp is also 26C with conductivity 50ms (at the current temp - 26C)". Thus the final readings we get from the aquarium would be lower than the actual ones. Or maybe I'm missing something?

[AQD_ottawa]

This is why you enter the temperature of the fluid at calibration so the computer can take into account the offset that you get from different temps. This is also why having the fluid at tank temp is so highly important for accuracy.

[VeL]

This is why you enter the temperature of the fluid at calibration so the computer can take into account the offset that you get from different temps. This is also why having the fluid at tank temp is so highly important for accuracy.

Thanks. However one thing I still do not fully understand. To take into account the offset from different temps, profilux is programmed to work with fluid 50ms@25C so it can calculate the ms accordingly to the different temps. Do I get it right? If so, when we use a 53ms@26.5 fluid (e.g. pinpoint's) the profilux will still treat it as 50ms@25C fluid and calibrate the probe wrong. Should I even try calibrating with my NSW fluid then?
I ask because even when I calibrate my probe within 0.2 range with the 50ms fluid, I still get 1.5ppm difference compared to my NSW 53ms@26.5 calibrated refractometer. At some point I start wondering which gives me the correct readings, P3eX or my refractometer... I tend to trust my probe but still wondering :headwally:

[AQD_ottawa]

UG not the refractomter connection again. Yes your refractometer might be calibrated to 53ms with NSW but if you try and read anything away from that exact set point with the refractometer the accuracy will drift due to the unit not designed to read NSW. The refractometer will only be accurate at 53mS.

If you use 53ms solution and enter 53ms into the calibration data entry the probe will calibrate accurate to 53Ms

IMPORTANT - A conductivity probe does not recognize the difference between NSW and NACL as it is measuring the conductance of the water NOT the refraction of the mineral content of the water. So it makes no difference with a conductivity monitor what type of fuid you use.

Compare the GHL probe against another high quality conductivity monitor ONLY then you will get a true comparison.

The 25 degrees on the bottle is for reference, the controller does not use this it uses its own offset and why you need to make sure both solution and tank temp are identical.

[VeL]

UG not the refractomter connection again. Yes your refractometer might be calibrated to 53ms with NSW but if you try and read anything away from that exact set point with the refractometer the accuracy will drift due to the unit not designed to read NSW. The refractometer will only be accurate at 53mS.

If you use 53ms solution and enter 53ms into the calibration data entry the probe will calibrate accurate to 53Ms

IMPORTANT - A conductivity probe does not recognize the difference between NSW and NACL as it is measuring the conductance of the water NOT the refraction of the mineral content of the water. So it makes no difference with a conductivity monitor what type of fuid you use.

Compare the GHL probe against another high quality conductivity monitor ONLY then you will get a true comparison.

The 25 degrees on the bottle is for reference, the controller does not use this it uses its own offset and why you need to make sure both solution and tank temp are identical.

Thanks Michael! Appreciate the response, cleared up a lot of stuff. Actually today I recalibrated my probe with a new recently purchased 50ms GHL fluid and this time I get only 0.5 ppm difference from my NSW calibrated refractometer. For now I will just leave it as is and will not bother calibrating with 53ms fluid. And thanks again, the provided info helped me understand quite a few things that bothered my mind lately.