Refractometers Vs Conductivity Probes/Readers/Etc

[Derrick Picker]

So I noticed today while doing some testing on my salinity the following. Please note that all items here were calibrated before testing.

Conductivity/Readers
Hanna Marine Salinity meter - 33.5PPT
Apex Neptune Conductivity Probe - 33.5PPT
Pinpoint Salinity Monitor - 33.5PPT

Refractometers
BRS Manual - 35PPT
Milwaukee Digital Refractometer - 35PPT.

What do I trust!! It is off by a clear 1PPT. Which one is actually correct. I realize either number is fine but I would still like to know. Do refractometers read higher than a conductivity probe?

What gives? Any ideas?

 

[Peace River]

Interesting question! Let’s see if we can get some help....

#reefsquad

 

[EmdeReef]

Milwaukee is known to give consistent but readings that are off a couple ppt.

Is your refractometer calibrated? Some refractometers require frequent calibration.

Assuming your 3 probes are calibrated; I would trust those over Milwaukee at least. I can speak to Hanna which is very close to my Orion conductivity meter and seems to hold calibration very well.

 

[saltyhog]

Wow, I'm impressed you have access to all those different units. Interested to hear what others think but I would trust the refractometers over the conductivity determinations. Very strange that they would be that far apart after calibration.

 

[homer1475]

I'm not sure as my miwaukee, hanna, and refractometer all read the same, when all are properly calibrated.

 

[HotRocks]

Wow, I'm impressed you have access to all those different units. Interested to hear what others think but I would trust the refractometers over the conductivity determinations. Very strange that they would be that far apart after calibration.

I have 2 refractometers that read exactly the same.

I have the hanna probe which also matches the refractometers exactly.

My Apex conductivity probe reads way high. Even after calibration. It reads in the 40.5ppt range while all of my other devices all consistently read 35ppt. The apex probe stays consistent, its just always 5 points high.

 

[EMeyer]

Can you describe the calibration process? Details I'm thinking about: calibration should be done with a standard solution (not DI water), and the calibration solutions are different for conductivity versus refractive index.

 

[dwest]

So I noticed today while doing some testing on my salinity the following. Please note that all items here were calibrated before testing.

Conductivity/Readers
Hanna Marine Salinity meter - 33.5PPT
Apex Neptune Conductivity Probe - 33.5PPT
Pinpoint Salinity Monitor - 33.5PPT

Refractometers
BRS Manual - 35PPT
Milwaukee Digital Refractometer - 35PPT.

What do I trust!! It is off by a clear 1PPT. Which one is actually correct. I realize either number is fine but I would still like to know. Do refractometers read higher than a conductivity probe?

What gives? Any ideas?

I check my Milwaukee periodically with 35 ppt reference solution. It always reads 36 ppt, so it may certainly run a little high ( that assumes my reference solution is “correct”). My Apex probe reads 35.5 ppt on average. To be honest, this is no difference than thermometers or any other measurement device or test kit. There is always error in measurement.

 

[Derrick Picker]

They were all calibrated before testing. However I used RODI for the refractometers. I purchased some calibration solution for those and will be retesting with it when I receive it. But I know for a fact currently all the refractometers are reading about 1.5ppt higher than the rest.

 

[Rick Mathew]

They were all calibrated before testing. However I used RODI for the refractometers. I purchased some calibration solution for those and will be retesting with it when I receive it. But I know for a fact currently all the refractometers are reading about 1.5ppt higher than the rest.

It is my understanding from what I read from Randy and also from experience that a refractometer calibrated with RODI will read 1 5 to 1.7 units higher...I calibrated with 35ppt salt water standard.. I can't do that with the Milwaukee ...at lease not that I know of...I also use the Hanna Salinity tester and find it quite good...I kind of use it as my go to measurement

 

[Derrick Picker]

So when I get the 35PPT solution and re-calibrate it should be dead on with the Hanna I presume?

 

[Joedubyk]

I'm not sure as my miwaukee, hanna, and refractometer all read the same, when all are properly calibrated.

Ditto. My Apex, refrac + Milwaukee are all on the same page.

 

[Derrick Picker]

Hmm. i must be doing something wrong then. I calibrated the Milwaukee and the manual refractometer with RODI. I also re-calibrated the Apex and the Hanna at the same time with their respective solutions.

 

[Joedubyk]

Hmm. i must be doing something wrong then. I calibrated the Milwaukee and the manual refractometer with RODI. I also re-calibrated the Apex and the Hanna at the same time with their respective solutions.

Milkwaukee should be calibrated with 35ppt solution

 

[Derrick Picker]

Milwaukee seems to only calibrate with a 0 solution. Are we talking about the same unit? The digital seawater refractometer?

 

[Joedubyk]

You might be right. I JUST calibrated one. Could've sworn it was 35 ppt though....My mind has been crazy with the new tank...

 

[DivingTheWorld]

I’ve tried a variety of electronics and devices to test salinity in my tank and they always vary some amount. The only thing I trust for sure is my Tropic Marin High Precision Hydrometer.

 

[aqua_code]

Is it possible your rodi water contains impurities that are causing miscalibration of the MA887?

This could explain the issue. Maybe you can try a 0 TDS solution to calibrate.

 

[Derrick Picker]

Is it possible your rodi water contains impurities that are causing miscalibration of the MA887?

This could explain the issue. Maybe you can try a 0 TDS solution to calibrate.

I have some distilled water I could try. Thats a great idea. I do have my RODI from my reservoir but also distilled.

 

[Derrick Picker]

BTW, I am using the water that comes with the Milwaukee to calibrate. Just FYI.