Apex Salinity Probe question

[beachsidereefer]

HI all,

Just bought a Apex salinity probe and calibration solution from BRS and followed the instruction in Apex to calibrate it. The probe settled at 34.9 PPT using the reference solution.
For years I've used a refractometer and I always calibrate it before each use and keep my salinity at 35 PPT.

What I'm trying to figure out is a significant variation between the two. Using my refractometer, I'm reading 35 PPT (the best I can tell), I even used a fresh bottle of calibration to make sure it wasn't stale solution. Apex is telling me my salinity is 37 ppt which is a significant deviation.

So I did an experiment, I drained about 3 gallons out and added 3 gallons of RO. my refractometer dropped to 34 PPT and Apex indicated 36.1. So at least the two devices are consistent when the salinity changed.

What I can't figure out, is which device is the correct measurement? Apex or the refractometer?

 

[piranhaman00]

Apex salinity probe is notoriously bad. Trust your refractometer.

 

[beachsidereefer]

great, and I paid 124 bucks for it so not a cheap investment.

 

[DS204]

Had the same variation as you. We had a Red Sea refractometer and the neptune probe was showing a different reading by about 3-4ppt.

Eventually we purchased a Hanna salinity checker to compare results. The Hanna + Red Sea refractometer read the same ppt, but the Neptune shows higher. Sort of disappointed as you are. Now, I just use the neptune probe to tell me when there are significant changes to the salinity. But, we use the Hanna to get a reliable reading.

 

[Amado]

Return the apex salinity probe if you can.
Buy the Hanna salinity checker it works

 

[SPR1968]

The best solution I’ve found it when your happy with your refractometer that the tank is at 35, calibrate the probe but when it says add to the solution, put it into the tank. Then it will match what
you trust

I use the Hanna salinity checker for the base reading now rather than refractometer

 

[beachsidereefer]

thanks all, so I'm going to assume my refractometer is the correct reading.