Hanna HI98319 and Milwaukee MA887 calibrated with DIY standard solution still showing different results

[jeremie]

I've always found that my Hanna salinity testers show lower results compared to the Milwaukee one, even after calibrated with the Hanna calibration solution. To clarify the issue, I prepared standards for both refractometers and conductivity meters with Randy's recipe in the lab I work at and tested them.

I mixed up 6.2g of NaCl with 182g of RODI to make a 3.29% solution for conductivity.

The 3.65% refractometer standard is made by mixing 3.65g of NaCl and 96.35g of RODI.

I then brought the solutions back home and conducted the experiments on the same day.

Here are my results:

	Milwaukee	Hand-held refractometer	Hanna A	Hanna B
testing standards	35 ppt (3.65% NaCl)	between 36~37 ppt (3.65% NaCl)	33.8 ppt (3.29% NaCl)	33.8 ppt (3.29% NaCl)
testing my reef tank	35 ppt	between 36~37 ppt	32.6 ppt	32.6 ppt

* Both Hanna testers were calibrated with their own bag of Hanna calibration solutions right before the test, and were cleaned with RODI water and dried out for 30 minutes.

* The Milwaukee tester and handheld refractometer were both calibrated with RODI water to 0 ppt before the test, and were allowed one minute for temperature equilibrium before collecting data during each test.

Does anyone have similar experiences with these instruments? It seems that Hanna has a different definition for S=35 seawater, which does not correspond to the typical 53 mS/cm at 25°C.

 

[taricha]

which of those things are conductivity meters?

Milwaukee

Hand-held refractometer

Hanna A

Hanna B

 

[jeremie]

which of those things are conductivity meters?

Milwaukee

Hand-held refractometer

Hanna A

Hanna B

Hanna A & B are both HI98319, which is a conductivity based salinity tester.

 

[Randy Holmes-Farley]

The problems may relate to inaccurate temperature corrections. Maybe try using all of them (all devices, calibration fluids, and tank water) at the same room temp.

 

[jeremie]

The problems may relate to inaccurate temperature corrections. Maybe try using all of them (all devices, calibration fluids, and tank water) at the same room temp.

I conducted all the tests on the same table in the same room. However, I shared the same concern since there were still variations in the temperature readings shown by the instruments, so I conducted another set of tests with similar results.

This time, I filled two beakers with seawater from the same tank, covered them to prevent evaporation, and then placed them in two rooms with different temperatures for one hour, and all the equipments were placed in the low/high temperature room for 30 minutes before testing. (I did not use DIY standards this time.)

I added another Hanna salinity meter to the test, so there's three of them now.

All the calibration of Hanna checkers were done in the low temperature room. (The calibration solutions were also placed in the room for one hour.

Here are the results:

Milwaukee tested in the low temperature room. (Calibrated with RODI to 0 ppt in the same room.)

Hanna checker (A) tested in the low temperature room.

Hanna checker (B) tested in the low temperature room.

Hanna checker (C) tested in the low temperature room.

Milwaukee tested in the high temperature room. (Calibrated with RODI to 0 ppt in the same room.)

Hanna checker (A) tested in the high temperature room.

Hanna checker (B) tested in the high temperature room.

Hanna checker (C) tested in the high temperature room.

	Milwaukee	Hanna A	Hanna B	Hanna C
24°C~25°C (75.2°F~77°F)	35 ppt	33.0 ppt	33.2 ppt	33.0 ppt
29°C~30°C (84.2°F~86°F)	35 ppt	32.9 ppt	32.9 ppt	32.9 ppt

 

[taricha]

So the hanna conductivity devices all read consistently with each other.
Just to confirm the most annoying scenario (good instruments - dodgy calibration standard), If you mix up a DIY conductivity standard, and calibrate the hanna's with that, will they then agree with your milwaukee about other standards and about your tank water?

 

[Randy Holmes-Farley]

The Milwaukee only claims +/- 2 ppt, though I’d hope for better if it reads 35 ppt correctly. That part looks good.

 

[jeremie]

So the hanna conductivity devices all read consistently with each other.
Just to confirm the most annoying scenario (good instruments - dodgy calibration standard), If you mix up a DIY conductivity standard, and calibrate the hanna's with that, will they then agree with your milwaukee about other standards and about your tank water?

I only did that on one of the Hanna testers, and the result did became closer to Milwaukee.

The same cup of seawater was tested by the Milwaukee and showed 35 ppt.

 

[jeremie]

The Milwaukee only claims +/- 2 ppt, though I’d hope for better if it reads 35 ppt correctly. That part looks good.

I'm also leaning more towards the results tested by Milwaukee. While I'm still kind of curious what is actually in the Hanna calibration solution? I tested it with Milwaukee, and the result showed 25 ppt. Are there any known solutions that match the same refractive index as a seawater sample with S=25?

 

[Randy Holmes-Farley]

I'm also leaning more towards the results tested by Milwaukee. While I'm still kind of curious what is actually in the Hanna calibration solution? I tested it with Milwaukee, and the result showed 25 ppt. Are there any known solutions that match the same refractive index as a seawater sample with S=25?

I have a hard time imagining what Hanna would use that has 53 mS/cm conductivity, but a refractive index matching only 25 ppt seawater.

 

[W31Olds]

I have a Hanna also and recently I purchased a Tropic Marin Hydrometer (gold Standard) and the Hanna reads about 2 ppt off (lower) after calibrating it so I just factor in the delta. I checked the manual and did not see any way to input an offset. I do get consistent readings from it though.

 

[RelaxingWithTheReef]

The Hanna Salinity tester itself does not seem all that bad, but the calibration standard they produce does not appear to be very accurate, or it drifts rapidly. Check out a previous post I did below.

I just mixed up a batch of the Randy Standard - 6.2g of NaCl with 182g of RODI to make a 3.29% solution for conductivity. After calibrating the Hanna to my Hach Salinity Standard (and applying a 0.5 ppt correction because my batch is certified as 34.5 ppt) the Randy Standard measured 34.8 ppt at 25 C. Given that Hanna has 0.1 ppt resolution, and always seems to drift a bit, I think this is pretty good. It’s important to calibrate Hanna at 25 C as the Hanna temperature compensation is not great.

I’m thinking that calibrating the Hanna with the Randy Standard will bring your Hanna reading within something like +- 0.2 ppt. You can also calibrate using the certified Hach standard if you like. But without going crazy, I don’t think you can ask for much better accuracy.

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(Previous post)
I was also frustrated with the Hanna Salinity Tester. With a calibrated Hanna, the Oceamo ICP-MS would always report around 1.1 ppt higher than the Hanna. Example - Hanna 35.0 ppt / ICP 36.1 ppt

I struck gold, and scored an awesome Orion model 135 conductivity / salinity meter. The Hach Salinity Standard 35.0 ppt #2714349 was used for calibration. Even though this is a premium standard, the tolerance of the standard is still 34-36 ppt. But, you can use the lot code on the bottle to retrieve the actual “Certificate of Analysis” for that batch from the Hach website. Turns out, my bottle of 35.0 ppt standard is certified as exactly 34.5 ppt.

The Orion is very accurate after calibration, provides a very stable reading, and the reading does not change with temperature. Now it was time to figure out what was going on with the Hanna.

After calibration, I measured the tank with the Orion and the Hanna. Sure enough, the Orion read 1.1 ppt higher than Hanna. The Orion matched the Oceamo ICP results!

Measuring the Hanna 35.0 ppt calibration solution at 25 deg C with the Orion, it measured 36.1 ppt. This is 1.1 ppt high, and probably explains why the Hanna tester is being calibrated in error to read 1.1 ppt low. FWIW – The Hanna accuracy specification is ±1.0 ppt for 0.0 - 40.0 ppt.

I was curious if the Hanna is able to compensate properly for temperature. Here are my tank water readings at different temperatures:

67.8 deg F, Orion = 34.9, Hanna = 34.1 (-1.1 ppt calibration error +0.3 ppt temp error)
78.4 deg F, Orion = 34.9, Hanna = 33.8 (-1.1 ppt calibration error)
88.9 deg F, Orion = 34.9, Hanna = 33.6 (-1.1 ppt calibration error -0.2 ppt temp error)

The Hanna thermometer is surprisingly accurate. Reading 79.4 deg compared to a Reference Thermometer reading of 79.42 deg. But, the temperature compensation is not that great in my opinion.

 

[jeremie]

I have a hard time imagining what Hanna would use that has 53 mS/cm conductivity, but a refractive index matching only 25 ppt seawater.

Could potassium chloride be a possibility?

 

[davidm777]

Does anyone have similar experiences with these instruments? It seems that Hanna has a different definition for S=35 seawater, which does not correspond to the typical 53 mS/cm at 25°C.

Thanks for digging into this. Back when I was searching for a tester I ran across this video. The guy mixes salt by weight and ran into same issues as you did with the Hanna testers. I am new to the hobby and I belong to a group that swears by the Hanna testers. Their tanks are amazing so this puzzled me. I just went with the Milwaukeeto play it safe, although by experience temperatures do play a big role.

 

[Randy Holmes-Farley]

Could potassium chloride be a possibility?

I doubt it, but have not checked. KCl is the most likely thing to use, but I expect it to impact refractive index more than sodium.

 

[jeremie]

I have a Hanna also and recently I purchased a Tropic Marin Hydrometer (gold Standard) and the Hanna reads about 2 ppt off (lower) after calibrating it so I just factor in the delta. I checked the manual and did not see any way to input an offset. I do get consistent readings from it though.

Thanks for digging into this. Back when I was searching for a tester I ran across this video. The guy mixes salt by weight and ran into same issues as you did with the Hanna testers. I am new to the hobby and I belong to a group that swears by the Hanna testers. Their tanks are amazing so this puzzled me. I just went with the Milwaukeeto play it safe, although by experience temperatures do play a big role.

The Hanna Salinity tester itself does not seem all that bad, but the calibration standard they produce does not appear to be very accurate, or it drifts rapidly. Check out a previous post I did below.

I just mixed up a batch of the Randy Standard - 6.2g of NaCl with 182g of RODI to make a 3.29% solution for conductivity. After calibrating the Hanna to my Hach Salinity Standard (and applying a 0.5 ppt correction because my batch is certified as 34.5 ppt) the Randy Standard measured 34.8 ppt at 25 C. Given that Hanna has 0.1 ppt resolution, and always seems to drift a bit, I think this is pretty good. It’s important to calibrate Hanna at 25 C as the Hanna temperature compensation is not great.

I’m thinking that calibrating the Hanna with the Randy Standard will bring your Hanna reading within something like +- 0.2 ppt. You can also calibrate using the certified Hach standard if you like. But without going crazy, I don’t think you can ask for much better accuracy.

-------------------------------
(Previous post)
I was also frustrated with the Hanna Salinity Tester. With a calibrated Hanna, the Oceamo ICP-MS would always report around 1.1 ppt higher than the Hanna. Example - Hanna 35.0 ppt / ICP 36.1 ppt

I struck gold, and scored an awesome Orion model 135 conductivity / salinity meter. The Hach Salinity Standard 35.0 ppt #2714349 was used for calibration. Even though this is a premium standard, the tolerance of the standard is still 34-36 ppt. But, you can use the lot code on the bottle to retrieve the actual “Certificate of Analysis” for that batch from the Hach website. Turns out, my bottle of 35.0 ppt standard is certified as exactly 34.5 ppt.

The Orion is very accurate after calibration, provides a very stable reading, and the reading does not change with temperature. Now it was time to figure out what was going on with the Hanna.

After calibration, I measured the tank with the Orion and the Hanna. Sure enough, the Orion read 1.1 ppt higher than Hanna. The Orion matched the Oceamo ICP results!

Measuring the Hanna 35.0 ppt calibration solution at 25 deg C with the Orion, it measured 36.1 ppt. This is 1.1 ppt high, and probably explains why the Hanna tester is being calibrated in error to read 1.1 ppt low. FWIW – The Hanna accuracy specification is ±1.0 ppt for 0.0 - 40.0 ppt.

I was curious if the Hanna is able to compensate properly for temperature. Here are my tank water readings at different temperatures:

67.8 deg F, Orion = 34.9, Hanna = 34.1 (-1.1 ppt calibration error +0.3 ppt temp error)
78.4 deg F, Orion = 34.9, Hanna = 33.8 (-1.1 ppt calibration error)
88.9 deg F, Orion = 34.9, Hanna = 33.6 (-1.1 ppt calibration error -0.2 ppt temp error)

The Hanna thermometer is surprisingly accurate. Reading 79.4 deg compared to a Reference Thermometer reading of 79.42 deg. But, the temperature compensation is not that great in my opinion.

It seems that the issue with the calibration solution is quite common. Perhaps the solution has evaporated slightly during manufacturing or packaging, causing the checker to give a lower reading.

I did also noticed that sometimes the reading can change after taking the checker out of the solution and putting it right back (both readings are stabilized), and the difference I’ve seen can be between 0.3 ppt to 0.5 ppt.

 

[jeremie]

The Hanna Salinity tester itself does not seem all that bad, but the calibration standard they produce does not appear to be very accurate, or it drifts rapidly. Check out a previous post I did below.

I just mixed up a batch of the Randy Standard - 6.2g of NaCl with 182g of RODI to make a 3.29% solution for conductivity. After calibrating the Hanna to my Hach Salinity Standard (and applying a 0.5 ppt correction because my batch is certified as 34.5 ppt) the Randy Standard measured 34.8 ppt at 25 C. Given that Hanna has 0.1 ppt resolution, and always seems to drift a bit, I think this is pretty good. It’s important to calibrate Hanna at 25 C as the Hanna temperature compensation is not great.

I’m thinking that calibrating the Hanna with the Randy Standard will bring your Hanna reading within something like +- 0.2 ppt. You can also calibrate using the certified Hach standard if you like. But without going crazy, I don’t think you can ask for much better accuracy.

-------------------------------
(Previous post)
I was also frustrated with the Hanna Salinity Tester. With a calibrated Hanna, the Oceamo ICP-MS would always report around 1.1 ppt higher than the Hanna. Example - Hanna 35.0 ppt / ICP 36.1 ppt

I struck gold, and scored an awesome Orion model 135 conductivity / salinity meter. The Hach Salinity Standard 35.0 ppt #2714349 was used for calibration. Even though this is a premium standard, the tolerance of the standard is still 34-36 ppt. But, you can use the lot code on the bottle to retrieve the actual “Certificate of Analysis” for that batch from the Hach website. Turns out, my bottle of 35.0 ppt standard is certified as exactly 34.5 ppt.

The Orion is very accurate after calibration, provides a very stable reading, and the reading does not change with temperature. Now it was time to figure out what was going on with the Hanna.

After calibration, I measured the tank with the Orion and the Hanna. Sure enough, the Orion read 1.1 ppt higher than Hanna. The Orion matched the Oceamo ICP results!

Measuring the Hanna 35.0 ppt calibration solution at 25 deg C with the Orion, it measured 36.1 ppt. This is 1.1 ppt high, and probably explains why the Hanna tester is being calibrated in error to read 1.1 ppt low. FWIW – The Hanna accuracy specification is ±1.0 ppt for 0.0 - 40.0 ppt.

I was curious if the Hanna is able to compensate properly for temperature. Here are my tank water readings at different temperatures:

67.8 deg F, Orion = 34.9, Hanna = 34.1 (-1.1 ppt calibration error +0.3 ppt temp error)
78.4 deg F, Orion = 34.9, Hanna = 33.8 (-1.1 ppt calibration error)
88.9 deg F, Orion = 34.9, Hanna = 33.6 (-1.1 ppt calibration error -0.2 ppt temp error)

The Hanna thermometer is surprisingly accurate. Reading 79.4 deg compared to a Reference Thermometer reading of 79.42 deg. But, the temperature compensation is not that great in my opinion.

Thanks for the information on temperature compensation. I didn’t notice much of a difference this time, but it’s probably due to the small temperature difference.

 

[RelaxingWithTheReef]

You may be on to something regarding evaporation. Hanna has a sealing problem with their Nitrate reagent where moisture gets in, and degrades the reagent. So it would not surprise me that there could be a similar problem with the salinity standard.

The Hanna tester has a pair of electrodes that tend to have micro bubbles on the surface at the start of the test or when calibrating. The bubbles will change the conductivity reading and cause error.

When calibrating it is important to agitate the tester quite a bit until the reading and temperature stabilize before pressing the Cal button. When testing the tank, I briskly sweep the tester around until the reading stabilizes. With this technique I don’t have any issues with repeatability. You should be able to get repeatability within 0.1 ppt.

 

[FernBluffReef]

My Hanna salinity checker measured about 1 low all the time. 34 vs actual 35. I found a lot of Hanna calibration fluid I got from my LFS was always low - likely has been sitting on the shelf a long time. A newer set of Hanna calibration fluid, ordered online from one of the major sellers, and it’s now reading much closer. .2 off testing this morning in comparison to a TropicMarine hydrometer. I was able to recalibrate using the LFS provided Hanna calibration fluid and the newer lot and reproduce the same reliably. I only purchased the TropicMarine due to this inconsistency to prove which was true. . Of course I have to note my inexpensive instant ocean swing hydrometer is also reliably within .2 of the TropicMarine meanwhile a refractometer is allover the place (me and refractometers just don’t get along)

So in closing, I’m thinking the Hanna salinity checker is better than I thought at first. It’s growing on me now that I have a better set of calibration packets.