Conductivity to Salinity Conversion

[ingchr1]

I have an Apera 5052 Saltwater Salinity Tester (https://aperainst.com/5052-saltwate...quariums-aquaculture-environmental-monitoring). The tester reads in PPT. It comes with a 50 mS/cm solution for calibration. When I calibrate the tester it flashes the 50 mS/cm then goes back to reading in PPT.

The potential issue is that when it goes back to PPT it reads 33.7 PPT. Should it read 32.7 PPT if the calibration point is 50 mS/cm?

I contacted them with this question and had to go several rounds of back and forth trying to get an adequate answer. What they final said was: "The discrepancy here comes from the conversions being factored. The formula you are using is ideal for measuring strictly for sodium chloride solutions (rendering the 32.7ppt), whereas our 5052 is engineered toward seawater for measuring salinity (thus rendering 33.7ppt instead)."

Is their explaination correct?

 

[Randy Holmes-Farley Verified Community Expert]

No.

50 mS/cm corrected to 25 deg C (or at 25 deg C) corresponds to a salinity under 33, as you note. I have a table here (Table 1)

http://reefkeeping.com/issues/2004-06/rhf/index.htm

You can also see it in this online calculator:

Practical Salinity Calculator – Salinometry

salinometry.com

 

[ingchr1]

Thank you @Randy Holmes-Farley

Wanted to make sure I wasn't off base as I'm still pushing them to get the proper response. I imagine the calibration point being off could have implications for them, and anyone using it.

A couple of responses I got back have been less than satisfying and a little surprising. Not sure of the technical background of the person I'm directly dealing with. Initial response was "This is a slightly more advanced question than we normally receive for our scientific instruments.". They final said they were going to reach out to their engineers, but it was after they reached out when I got the explanation provided in my initial post.

The tester does work well and I also have a pH tester from them that also works well. Being exactly 1 PPT off, I can only guess how the error may have occurred. I hope to get a straight answer out of them on this.

I actually followed your article to make a 33.7 PPT solution to calibrate this tester. What I did was calibrate it in a 50 mS/cm solution that I had, then I made a solution until the unit read 34.7 PPT. Then recalibrated it with that solution. The meter reads what my controller probe reads.

Here's the certificate that came with it.