Confusing measurements from refractometer and hanna sanity tester (conductivity)

[micl10]

I'm trying to make my saltwater mixing life a little easier so I got a Hanna sanity checker. I'm trying to figure out if I've properly calibrated it and it sent me into a rabbit hole.

So i have 2 samples:
#1 Freshly mixed saltwater
#2 My current tank

I have 2 instruments:
#1 5 year old refractometer (the hinge is a bit stiff, but otherwise seem good, i doubt these things really "get old", calibrated using "accubrate")
#2 New Hanna Checker

Both have been freshly calibrated. All my hanna readings are sampled in a plastic cup. All my refractometer readings are pulled from the tank, brute, and calibration bottle into a pipette...allowed to come to room temperature, then read in the refractometer.

My freshly mixed tub of saltwater reads 34.8ppt with the hanna. It reads about 38ppt with the refractometer
My tank water (originally mixed using the refractometer) reads 34ppt using my refractometer, and a whopping 31.8 from my hanna checker.

Which one do I trust here, lol. I recalibrated the hanna twice using 2 packets. Do I just have a bad batch of accubrate. Are my newly purchased fishes/shrimp (thankfully no corals yet) in any mortal danger?

 

[Reefing.with.Rich]

I’m in the same position lol. Iv always used the Milwaukee salinity checker(but also always have a look through refractometer)
I have a buddy whole showed me his Hanna salinity checker and it is just so much quicker to use than the Milwaukee so I picked on up. The Hanna checker always shows at least .02-.03
Milwaukee shows 1.026 today and my Hanna should show 1.024 and the last minute drop to 1.023 before I pull it from the tank. So I’m just as confused on which is the most accurate number

 

[gbroadbridge]

I'm trying to make my saltwater mixing life a little easier so I got a Hanna sanity checker. I'm trying to figure out if I've properly calibrated it and it sent me into a rabbit hole.

So i have 2 samples:
#1 Freshly mixed saltwater
#2 My current tank

I have 2 instruments:
#1 5 year old refractometer (the hinge is a bit stiff, but otherwise seem good, i doubt these things really "get old", calibrated using "accubrate")
#2 New Hanna Checker

Both have been freshly calibrated. All my hanna readings are sampled in a plastic cup. All my refractometer readings are pulled from the tank, brute, and calibration bottle into a pipette...allowed to come to room temperature, then read in the refractometer.

My freshly mixed tub of saltwater reads 34.8ppt with the hanna. It reads about 38ppt with the refractometer
My tank water (originally mixed using the refractometer) reads 34ppt using my refractometer, and a whopping 31.8 from my hanna checker.

Which one do I trust here, lol. I recalibrated the hanna twice using 2 packets. Do I just have a bad batch of accubrate. Are my newly purchased fishes/shrimp (thankfully no corals yet) in any mortal danger?

When you calibrate the Hanna, you need to float the sachet in the sump to get it up to 25deg C (77 deg F) as it is only 35ppt at that temperature. You need to measure the salinity of the tank water at the same temperature.

Did you do it that way?

 

[micl10]

The Hanna has a temperature probe. The instructions didn't ask for that.

And yes I did the refractometer tests while the samples are the same temp

 

[Salty_Northerner]

I was in the same boat just not too long ago. Calibrated the hanna tester and I was showing quite low on actual SG. Refractometer after calibration showed 38. I 2 went down the rabbit hole..

I Pulled out a couple older swing arm salinity testers and found them to be reading on the lower side so I placed that hanna calibration fluid packet into the tank and let it sit for probably 30 minutes. And then quickly cut the packet open and dropped the whole unit in the fluid and waited until the temperature stabilized and then I hit calibrate. I then mixed up some new saltwater and checked it with the Hannah and also the refractometer and was surprised it was trash. It was only 4 months old and was inaccurate from day one I'm thinking.

I then bought a tropic Marin high precision hydrometer and the Hannah tester is pretty much bang on with the tropic Marin hydrometer.

So that ended my venture down the rabbit hole and can take a sigh of relief now knowing that the tester from Hannah is actually very accurate.

As for the Milwaukee salinity tester you should be covering the hole after you drop your water in since there is a very small light inside there and any ambient light will screw around with its actual reading.

 

[gbroadbridge]

The Hanna has a temperature probe. The instructions didn't ask for that.

And yes I did the refractometer tests while the samples are the same temp

Yes, I know the instructions don't state you need to have the calibration solution at 25 deg C - they are incorrect.

The profile normally printed on the back of the calibration solution does show the temperature variation - however as it is a solution of Potassium Chloride you do need to calibrate at 25 deg C otherwise the calibration will be incorrect.

The temperature correction only works correctly when initially calibrated correctly

 

[Randy Holmes-Farley]

Yes, I know the instructions don't state you need to have the calibration solution at 25 deg C - they are incorrect.

The profile normally printed on the back of the calibration solution does show the temperature variation - however as it is a solution of Potassium Chloride you do need to calibrate at 25 deg C otherwise the calibration will be incorrect.

The temperature correction only works correctly when initially calibrated correctly

I don't agree. Why would that be necessary? It certainly wasn't necessary with other conductivity meters I've had.

Unless the fluid in the pouch has a substantially different change in conductivity with temp than does seawater (which is fairly unlikely), then the automatic temperature compensation for changes in conductivity with temperature will work both for calibriaton and in measurement.

The temp correction is simple mathematical correction that gets applied all the time.

the same rationale applies to AYC refractometers, which oddly state it must be calibrated at a fixed temp, which makes zero sense since it is a physical correction mechanism that you cannot defeat.

 

[gbroadbridge]

I don't agree. Why would that be necessary? It certainly wasn't necessary with other conductivity meters I've had.

Unless the fluid in the pouch has a substantially different change in conductivity with temp than does seawater (which is fairly unlikely), then the automatic temperature compensation for changes in conductivity with temperature will work both for calibriaton and in measurement.

The temp correction is simple mathematical correction that gets applied all the time.

the same rationale applies to AYC refractometers, which oddly state it must be calibrated at a fixed temp, which makes zero sense since it is a physical correction mechanism that you cannot defeat.

Thanks Randy

I understand how it's meant to work - I'm just explaining how it works with the Hanna Salinity tester.
Believe me, it caused me a lot of frustration.
I'm not sure how their temperature correction has been designed but it appears to be flawed.

I've confirmed the behaviour with 3 other checkers and they all behave the same.
I raised the issue with Hanna Tech Support and they confirmed that the device must be calibrated at 25 deg C

See below for an illustration.

As you can see the temperature is measured correctly, but the result varies with temperature.

 

[micl10]

Thanks Randy

I understand how it's meant to work - I'm just explaining how it works with the Hanna Salinity tester.
Believe me, it caused me a lot of frustration.
I'm not sure how their temperature correction has been designed but it appears to be flawed.

I've confirmed the behaviour with 3 other checkers and they all behave the same.
I raised the issue with Hanna Tech Support and they confirmed that the device must be calibrated at 25 deg C

See below for an illustration.

As you can see the temperature is measured correctly, but the result varies with temperature.

If true, that's unfortunate. Because "calibrating" the packet to a known temperature, means my tank's temperature has to also be calibrated, and then there's still the accuracy of whatever the +/- of the water is to that temperature.

Too many levels of errors that can happen there.

Anyway, I went to my local LFS and it seems like the Hanna is measuring low for me. The refractometer was more "correct". This of course is assuming my LFS is making their saltwater correctly.

At the end, I just bought myself a tropic marin hygrometer. I hear that it is very fragile, so what I'll do is use that, as well as my refractometer to calibrate my Hanna. Fortunately, the Hanna seems to be fairly precise/repeatable as far as it's measurements, so it'll be my daily go-to for sampling salinity.

 

[gbroadbridge]

If true, that's unfortunate. Because "calibrating" the packet to a known temperature, means my tank's temperature has to also be calibrated, and then there's still the accuracy of whatever the +/- of the water is to that temperature.

Too many levels of errors that can happen there.

Anyway, I went to my local LFS and it seems like the Hanna is measuring low for me. The refractometer was more "correct". This of course is assuming my LFS is making their saltwater correctly.

At the end, I just bought myself a tropic marin hygrometer. I hear that it is very fragile, so what I'll do is use that, as well as my refractometer to calibrate my Hanna. Fortunately, the Hanna seems to be fairly precise/repeatable as far as it's measurements, so it'll be my daily go-to for sampling salinity.

It works well enough as long as you are within a few degrees, just calibrate at the tank temperature.
Where it fails terribly is if you use a cold calibration fluid (like 15-20 degrees C) and then test the tank which is at 25-26.

You can test your own checker easily - perhaps they've fixed the firmware.

 

[gbroadbridge]

I don't agree. Why would that be necessary? It certainly wasn't necessary with other conductivity meters I've had.

Unless the fluid in the pouch has a substantially different change in conductivity with temp than does seawater (which is fairly unlikely), then the automatic temperature compensation for changes in conductivity with temperature will work both for calibriaton and in measurement.

The temp correction is simple mathematical correction that gets applied all the time.

the same rationale applies to AYC refractometers, which oddly state it must be calibrated at a fixed temp, which makes zero sense since it is a physical correction mechanism that you cannot defeat.

Followup:

Just noticed Hanna have updated/changed the SKU for the calibration fluid and now make clear it is to be used at 25 deg C

 

[Salty_Northerner]

Thanks Randy

I understand how it's meant to work - I'm just explaining how it works with the Hanna Salinity tester.
Believe me, it caused me a lot of frustration.
I'm not sure how their temperature correction has been designed but it appears to be flawed.

I've confirmed the behaviour with 3 other checkers and they all behave the same.
I raised the issue with Hanna Tech Support and they confirmed that the device must be calibrated at 25 deg C

See below for an illustration.

As you can see the temperature is measured correctly, but the result varies with temperature.

Do yourself a favor and grab the Neptune conductivity calibration fluid.

TM high precision hydrometer tested with tank water in a 500ml graduated cylinder read 1.026 and when using the Hanna calibration fluid the Hanna tester did read 1.026 BUT when checking in the tank it was reading 1.025

Using the Neptune calibration fluid it calibrated to 1.026 and then checked in the tank and it was exactly 1.026 bang on.

I just tossed the pouch into the tank to float around for 10 min and then calibrated it. Reads exactly what the TM does, honestly give it a try

This stuff from BRS

 

[Randy Holmes-Farley]

Followup:

Just noticed Hanna have updated/changed the SKU for the calibration fluid and now make clear it is to be used at 25 deg C

Either the product is badly designed (e.g., it doesn't use its own temperature compensation during calibration, why not?), the fluid they use has a grossly different temperature vs conductivity profile than seawater, or they are misunderstanding their own product.

Have you tried to calibrate at a substantially different temp than 25 deg C (say, 20 deg C), and then cannot read the calibration fluid correctly at that same temp? if so, then that indicates they turn off the temp correction during calibration but it is back on during normal measurement.

 

[Salty_Northerner]

Maybe the user can check the certificate that comes with the unit as it shows the temperature it was @ during certification.. let me see what mine shows and I'll snap a photo of it.

 

[Salty_Northerner]

 

[micl10]

final update:

i just got my TM hydrometer, and confirmed my suspicion. i used my now-calibrated-against-my-reefractometer Hanna to mix saltwater to 35ppt. floated the hydrometer on that and read 1.0256 at 77.8F, which is 34.20 SG adjusted to 77F.

I mixed the tub to [email protected], calibrated the hanna against that and now I can sleep at night.

Just for context, my tank is a 20g nano, and my skimmer is still a bit touchy so my ATO is a bit overactive lately, so i'm a bit paranoid about my salinity. so yes, i am crazy, but not THAT crazy.

PS: Corina Pop also inspected my device. I'm gonna have to Karen and ask to see her manager.

 

[gbroadbridge]

Either the product is badly designed (e.g., it doesn't use its own temperature compensation during calibration, why not?), the fluid they use has a grossly different temperature vs conductivity profile than seawater, or they are misunderstanding their own product.

Have you tried to calibrate at a substantially different temp than 25 deg C (say, 20 deg C), and then cannot read the calibration fluid correctly at that same temp? if so, then that indicates they turn off the temp correction during calibration but it is back on during normal measurement.

If you calibrate and measure at the same temperature it reads correctly.

Something is awry somewhere, and perhaps the firmware has been updated to fix it.

I simply suggest that folks calibrate at the tank temperature, and it then operates correctly - but the ATC does not work.

 

[gbroadbridge]

That agrees with what I'm saying

 

[Randy Holmes-Farley]

I still do not understand whether it uses its ATC during calibration or not,.

If you calibrate using the 35 ppt standard packet at, say, 20 deg C, and read that same packet at 25 deg C, does it read 35 ppt, or something else?

 

[micl10]

I still do not understand whether it uses its ATC during calibration or not,.

If you calibrate using the 35 ppt standard packet at, say, 20 deg C, and read that same packet at 25 deg C, does it read 35 ppt, or something else?

I did this experiment at 77F and 71F and the hanna read the same packet nearly the same. Iirc there was a only 0.4 difference.