Salinity measurements are coconuts.

aircrane1 · Jan 17, 2019

I just bought a Hanna digital salinity tester and it read my DT at 1.021. Refractometer (from Marine Depot) reads 1.024-1.025 (old eyes have a hard time with the lines). Apex reads 1.0267. I have been relying on the refractometer since it's the lowest tech thing I have and I tend to consider these things as a reliable baseline. Now i'm wondering just which ones are lying to me. Calibrated everything properly a far as I can discern.

There really aren't any LFS's in my area to take a sample to and I wish I could get the issue nailed down ASAP but not sure which direction to go.

Any help would be very much appreciated.

Big G · Jan 17, 2019

From Hanna's website: accuracy = ±1 ppt for 0.0 to 40.0 ppt;

JimWelsh · Jan 17, 2019

aircrane1 said:
Calibrated everything properly a far as I can discern.

How did you calibrate the refractometer: using pure water (distilled, RO/DI, etc.), or using a refraction standard that targets 35 PPT? Did you calibrate the Apex and the Hanna using the same conductivity standard, or each using different standards? How much attention did you pay to the temperature of the conductivity standards when you calibrate the Apex and the Hanna?

aircrane1 · Jan 17, 2019

JimWelsh said:
How did you calibrate the refractometer: using pure water (distilled, RO/DI, etc.), or using a refraction standard that targets 35 PPT? Did you calibrate the Apex and the Hanna using the same conductivity standard, or each using different standards? How much attention did you pay to the temperature of the conductivity standards when you calibrate the Apex and the Hanna?

I calibrated the refractometer using RO/DI and the Hanna and APEX using the solutions provided. Tried to follow the directions for each as close as possible, Now that you mention it, I rinsed the Hanna in pretty cold RO/DI this evening when calibrating. The Hanna and APEX used different conductivity standards as far as I know (the solutions for calibation both came from the manufacutrers) but I apologize if I don't actually understand your reference to standards.

JimWelsh · Jan 17, 2019

For the refractometer, please see: http://www.reefkeeping.com/issues/2004-06/rhf/ and for why you should use that instead of RO/DI (despite what the manufacturer's instructions say) see https://www.reef2reef.com/ams/refractometers-and-salinity-measurement.5/

The Apex and Hanna both appear to use a 35 PPT / 53 mS conductivity standard, so you should be able to calibrate them at the same time with the same standard. There is some consensus in the Apex community that the standard should be equilibriated with your tank temperature when you calibrate the Apex probe. The Hanna probably wants to be at 25C when you calibrate. Hopefully, you run your tank at 25C (77F).

aircrane1 · Jan 17, 2019

I currently run the tank at 77.5-78 as controled by the APEX. I bought some extra calibration solution for the APEX and I think I will try recalibrating every tool I have at my disposal (Hanna came with a bunch of calibration fluid packets). Maybe I need to send a sample off for a complete baseline for all of my parameters?!?

Randy Holmes-Farley · Jan 20, 2019

aircrane1 said:
I currently run the tank at 77.5-78 as controled by the APEX. I bought some extra calibration solution for the APEX and I think I will try recalibrating every tool I have at my disposal (Hanna came with a bunch of calibration fluid packets). Maybe I need to send a sample off for a complete baseline for all of my parameters?!?

For salinity, you need not get such a measurement. Just buy or make a salinity standard and calibrate your methods.