Salinity Measurement

[GammaYankee]

TLDR: Hanna salinity checker result is quite different from refractometer result. Which one should I trust?

Today, I decided to calibrate my refractometer and Hanna salinity checker. I calibrated my refractometer using BRS refracto juice, and cross validated with RODI water and brightwell calibration fluid. Everything looked good. I then calibrated my hanna checker with the Hanna calibration fluid, looks okay. Here comes the funny thing.

I decided to put a few drops of hanna calibration fluid to my freshly calibrated refractometer, and it reads 1.020. Then, I checked my tank water, refractometer reads 1.029 while Hanna reads 1.026. And my Apex reads 1.026, but I haven't calibrated my Apex salinity probe for a while. My previous ICP gives 35.66 which is 1.027.

I am so confused now, which one should I trust? It's really surprising that I cannot even properly measure such a basic parameter, after spending so much money into testing...

 

[Rainblood]

Tropic Marin Hydrometer

Tropic Marin Hydrometer

aquacave.com

 

[Steve Burton]

Tropic Marin Hydrometer

Tropic Marin Hydrometer

aquacave.com

This is what I use to periodically calibrate my Refractometer

 

[shanepike]

From what I've read, the calibration fluids for a refractometer and Hannah checker are completely different, because the Hannah checker is based on conductivity while the refractometer is based on light shift. You can't interchange the calibration fluids.

 

[jcook54]

I use my Hanna checker most of the time. But i trust my refractometer more. Here's what I do:

• Calibrate refractometer.
• Calibrate Hanna checker.
• Trust the refractometer and adjust the Hanna accordingly.
• In my case I shoot for 1.025 salinity.
• When it's dead on using the refractometer, the Hanna checker reads 1.022.
• When I mix saltwater I use the Hanna and shoot for a reading of 1.022 with the understanding that the refractometer will read 1.025.

I'll calibrate everything in this way once or twice a year. The Hanna is my go-to and I calibrate it more often than that. The main goal for me is consistency. If everything is a little off then at least the salinity is consistent.

 

[wadadligem]

Refracto

 

[GammaYankee]

From what I've read, the calibration fluids for a refractometer and Hannah checker are completely different, because the Hannah checker is based on conductivity while the refractometer is based on light shift. You can't interchange the calibration fluids.

That was what I was expecting. So the Hannah calibration reading 1.20 with refractometer does not upset me too much. But the inconsistency in tank water measurement is frustrating.

 

[GammaYankee]

I use my Hanna checker most of the time. But i trust my refractometer more. Here's what I do:

• Calibrate refractometer.
• Calibrate Hanna checker.
• Trust the refractometer and adjust the Hanna accordingly.
• In my case I shoot for 1.025 salinity.
• When it's dead on using the refractometer, the Hanna checker reads 1.022.
• When I mix saltwater I use the Hanna and shoot for a reading of 1.022 with the understanding that the refractometer will read 1.025.

I'll calibrate everything in this way once or twice a year. The Hanna is my go-to and I calibrate it more often than that. The main goal for me is consistency. If everything is a little off then at least the salinity is consistent.

I was doing that with my hannah. So I always measure my tank water with hanna and when I make my salt water, I tried to match the salinity with Hannah again. But then overtime, the error would grow, since such type of measurement is not on an absolute scale.
Overall, things are okay, like my ICP test came back with 35.5 ppt. But it's scary when I read 1.29 with my refracto.