Why do my Salinity measurements vary by 0.002 sg between refractometer and conductivity testers?

[TheHunterYall]

I’m currently lost in this sauce now to. My spread is large. Makes me wonder if my conductivity is low? I have calibrated Hanna to it’s packets and it also reads dead on 1.026 for the refract cal solution, AccuBrate. Refractometer also calibrated to same AccuBrate. Both read 0 at RODI FWIW. Tank water reads 1.025 for refrac and 1.021 for Hanna, what the heck? That seems outside the accuracy’s...hence is there something else going on in the chemistry? Alk is 6.8, ph is 7.8.

 

[TheHunterYall]

I’m currently lost in this sauce now to. My spread is large. Makes me wonder if my conductivity is low? I have calibrated Hanna to it’s packets and it also reads dead on 1.026 for the refract cal solution, AccuBrate. Refractometer also calibrated to same AccuBrate. Both read 0 at RODI FWIW. Tank water reads 1.025 for refrac and 1.021 for Hanna, what the heck? That seems outside the accuracy’s...hence is there something else going on in the chemistry? Alk is 6.8, ph is 7.8.

ORP is lowish too, 250. Also I tend to trust the refractometer. But want to use and switch to the Hanna. But may send it back...

 

[Randy Holmes-Farley]

I’m currently lost in this sauce now to. My spread is large. Makes me wonder if my conductivity is low? I have calibrated Hanna to it’s packets and it also reads dead on 1.026 for the refract cal solution, AccuBrate. Refractometer also calibrated to same AccuBrate. Both read 0 at RODI FWIW. Tank water reads 1.025 for refrac and 1.021 for Hanna, what the heck? That seems outside the accuracy’s...hence is there something else going on in the chemistry? Alk is 6.8, ph is 7.8.

Many meters have a substantial error range with would include +/- 0.002 sg. The Hanna 98319, for example, only claims +/- 1 ppt. A digital reading does not mean high accuracy.

Conductivity meters and refractometer standards cannot always read their respective calibration solutions correctly, unless it is a seawater composition mimic.

For example, my DIY standard using sodium chloride are different for refractometers, hydrometers, and conductivity meters, each designed to get the appropriate device to correctly read 35 ppt seawater.

This has more:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

 

[Tim Olson]

I feel your pain. Here's some ideas that should help improve the calibration process.

• First and foremost, listen to Randy Holmes-Farley. He's clearly the expert on this.
• It looks like AccuBrate is only meant to calibrate refractometers, so only use it to calibrate your refractometer. You shouldn't use it to check the Hanna salinity tester.
• Calibrating the Hanna salinity checker with the Hanna packets, should be reasonably accurate.
• In the end, I ended up using Accura Sea to calibrate my refractometer and a Lab made Randy Holmes-Farley refractor standard. I also used Accura Sea to calibrate my Hanna Salinity Tester

Here was my summary from earlier in this thread.

Update - I believe that I now have a fully calibrated refractometer (VEE GEE STX-3) and Hanna Salinity Tester (HI98319).

For the refractometer calibration, I ended up using 2 standards, including "AccuraSea Seawater Reference/Calibration Solution” and a lab-made Randy Holmes-Farley refractometer standard that @mtfish graciously sent me.

The result is my refractometer is calibrated as accurately as possible. Also, the VEE GEE STX-3 is very easy to read compared to my less expensive refractometer, with the view screen being about twice the size. Therefore, I can get reasonably precise readings.

Also, I calibrated the Hanna Salinity Tester (HI98319) with the AccuraSea standard, which worked out great. Before, I calibrated it with Hanna's standard that was provided with the tester. Although, it would always read about 0.0013 sg low, compared to the refractometer. Now, it correlates perfectly with the refractometer.

Overall, I'm excited that I can finally measure salinity accurately and precisely. Of course, within in the device tolerances.

So, thank you all once again for all the help on this. I never could have done it on my own.

I hope this helps some.

 

[TheHunterYall]

Many meters have a substantial error range with would include +/- 0.002 sg. The Hanna 98319, for example, only claims +/- 1 ppt. A digital reading does not mean high accuracy.

Conductivity meters and refractometer standards cannot always read their respective calibration solutions correctly, unless it is a seawater composition mimic.

For example, my DIY standard using sodium chloride are different for refractometers, hydrometers, and conductivity meters, each designed to get the appropriate device to correctly read 35 ppt seawater.

This has more:

Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

The Hanna cal solution says 35 ppt. The AccuBrate says 1.0264, 35 ppt, and 53 mS/cm at 25c

Hanna reads the AccuBrate spot on.

I’m going to try the hand made solutions.

 

[TheHunterYall]

The Hanna cal solution says 35 ppt. The AccuBrate says 1.0264, 35 ppt, and 53 mS/cm at 25c

Hanna reads the AccuBrate spot on.

I’m going to try the hand made solutions.

Also, Hanna claims +\- .001sg. But I’ve been looking at ppt as well. Same deal. Just thought I would get within .002 this way, I would claim success then.

 

[TheHunterYall]

Also, Hanna claims +\- .001sg. But I’ve been looking at ppt as well. Same deal. Just thought I would get within .002 this way, I would claim success then.

Long story short I got the Amazon scale, checked its cal, .01g. Made the hand standards. I ended up tweaking the Hanna and the refractometer, probably close to their average. They now match for my tank and LFS water as a third standard.

I guess I don’t really trust any of the bottled standards I have anyway...

Moving on with my life!

Thanks guys, couldn’t have done it without you!

 

[Tim Olson]

Long story short I got the Amazon scale, checked its cal, .01g. Made the hand standards. I ended up tweaking the Hanna and the refractometer, probably close to their average. They now match for my tank and LFS water as a third standard.

I guess I don’t really trust any of the bottled standards I have anyway...

Moving on with my life!

Thanks guys, couldn’t have done it without you!

Sounds like a good plan. As long as the salinity is in range, now you just have to keep it stable.

All the best!

 

[Jeepjeep_0]

Love, it!! The amount of time and money and all comes down to a $20 scale and some table salt. I pulled my hair out over this and came to the same resolution. Hats off to Mr. Holmes Farley!!!