Salinity measurement issues

[aSaltyKlown]

I have a Tropic Marin Hydrometer, two refractometers - both from BRS, one about 4 years old the other about 10 years old, Hanna Salinity checker and an Instant Ocean swing arm hydrometer. I've been mainly using the Hanna Salinity checker to measure my water change container. It has always been ok to use, or at least I thought. I decided to calibrate and double check with the refractometers and the TM. So, I calibrated one refractometer with Randy's DIY solution and one with Fritz 35ppt. I calibrated the Hanna with the Hanna fluid.

All 5 are measuring about the same in my display tank. The first pics are the display. The Hanna shows the tank is 75.8, but the Apex and handheld thermometer is showing 79.


Then I go down to check the SW container and this is where things get interesting.
The Hanna is showing 1.027 @ 72, the handheld thermometer is 74.5. The TM is showing 1.039, and both refractometers are showing about 1.024. The swing arm is showing about 1.025. I'm using the hamzasreef salinity correction calculator, and it says that the actual reading would be 1.0386 on the TM, so the temperature would not throw it off as much as it is showing.


I know that I won't get the same readings from all 5 and hear that the TM should be considered king. However, I've calibrated the 3 that I can, of those 3 I trust the Hanna the least. I've just ordered a 500ml graduated cylinder so I can make more diy solution to test the TM.

I'm at a loss right now and am holding off the water change. Could the TM be off or is it the others or is it something in the holding bin? Again, all 5 were about the same in the display.

Thanks

 

[Llyod276]

Bruh for calibrating why don't you just use distilled water??? Forget all that fancy stuff. Keep it simple doode!

 

[FernBluffReef]

I have a Tropic Marin Hydrometer, two refractometers - both from BRS, one about 4 years old the other about 10 years old, Hanna Salinity checker and an Instant Ocean swing arm hydrometer. I've been mainly using the Hanna Salinity checker to measure my water change container. It has always been ok to use, or at least I thought. I decided to calibrate and double check with the refractometers and the TM. So, I calibrated one refractometer with Randy's DIY solution and one with Fritz 35ppt. I calibrated the Hanna with the Hanna fluid.

All 5 are measuring about the same in my display tank. The first pics are the display. The Hanna shows the tank is 75.8, but the Apex and handheld thermometer is showing 79.


Then I go down to check the SW container and this is where things get interesting.
The Hanna is showing 1.027 @ 72, the handheld thermometer is 74.5. The TM is showing 1.039, and both refractometers are showing about 1.024. The swing arm is showing about 1.025. I'm using the hamzasreef salinity correction calculator, and it says that the actual reading would be 1.0386 on the TM, so the temperature would not throw it off as much as it is showing.


I know that I won't get the same readings from all 5 and hear that the TM should be considered king. However, I've calibrated the 3 that I can, of those 3 I trust the Hanna the least. I've just ordered a 500ml graduated cylinder so I can make more diy solution to test the TM.

I'm at a loss right now and am holding off the water change. Could the TM be off or is it the others or is it something in the holding bin? Again, all 5 were about the same in the display.

Thanks

Following: as I have the same concern

I just got Tropic Marin as a gold standard reference. I also don’t have a dedicated cylinder quite yet.

I floated the tropic marine in the tank (pumps off and 76.9 degrees per multiple sensors.). My Instant Ocean (which I trust says 34.8). Hanna just calibrated says 34.0 which is norm - Hanna is generally 1.0 low. TropicMarine (converted) says 37.2. Refractometer I will not use as too flaky. Last ICP showed my Instant Ocean being spot on so it remains my reference and I can reliably correlate to the Hanna.

I was mixing salt. So I also tested my newly mixed. Hanna 32.2. Tropic Marine. 37 (floated in my mixing station with pumps off). Temp was around 75 if memory services me right. I added more salt to bring to 34 on Hanna which is where I wanted to match my tank. Tropic Marine didn’t move, remained 37. I proceeded with my water charge disregarding the Tropic Marine.

I’m real curious what I’m doing wrong with the Tropic Marine also. I also still have to get a graduated cylinder but I should still be able to float with pumps off and get a close reading. I’ve never had one. Agreed it should be trusted but for the moment I’m wondering what I did wrong as I, confident based on the above that the readings I got are not right. First use

 

[Randy Holmes-Farley]

Bruh for calibrating why don't you just use distilled water??? Forget all that fancy stuff. Keep it simple doode!

Because it is often inherently inaccurate!

 

[Llyod276]

Ah, I see. Nothing simple can possibly the correct answer. Ok.
I apologize in the assumption that "often" has the same meaning as "always."

 

[hoffmeyerz]

Pick ONE tester and stick with it. Calibrate it and read it the same way every time. It's best to be consistent even if you are running slightly off from your reading.
The Tropic Marine floating hydrometer is great because it is calibrated during its construction to read our target range specifically and needs no further calibration. You can float it in the tank (I do) just remember it is calibrated for 77F.
Calibrating refractometers with distilled or ro/di can cause inaccuracies because it is calibrating to zero, not your target range. The further you read from calibration the larger the error swing.

 

[aSaltyKlown]

Pick ONE tester and stick with it. Calibrate it and read it the same way every time. It's best to be consistent even if you are running slightly off from your reading.
The Tropic Marine floating hydrometer is great because it is calibrated during its construction to read our target range specifically and needs no further calibration. You can float it in the tank (I do) just remember it is calibrated for 77F.
Calibrating refractometers with distilled or ro/di can cause inaccuracies because it is calibrating to zero, not your target range. The further you read from calibration the larger the error swing.

I generally do, using the Hanna, both display's were always at 1.026 as was new SW. It's when I decided to check the displays with the TM and refracto's is when I got readings of 1.040. took care of that and got it down to .025. As mentioned, similar readings across all tools in my displays now, but a big margin in the new SW. Not sure what to trust.

 

[hoffmeyerz]

Not sure what to trust.

Personally I trust my TM. I also have a refractometer but I only use it for quick checks and I calibrate it off of the TM readings.
I get my mixing barrel up to 77F before adding salt and mix till I get 1.026 on the TM. When checking the tank I turn off all pumps and float the TM in the tank. When I check sal of bag water a new fish is in I use the refractometer that I periodically calibrate with the TM.

 

[Randy Holmes-Farley]

Ah, I see. Nothing simple can possibly the correct answer. Ok.
I apologize in the assumption that "often" has the same meaning as "always."

Not sure if you are being sarcastic, but it is true that most refractometers are not correctly calibrated with ro/di water, despite manufacturer claims. That is because they were not designed to be used in seawater, unless they state they are true seawater refractometers. They were designed for sodium chloride brine solutions.

That mismatch can be overcome with a 35 ppt seawater standard for calibration. They will then be accurate for measurement of 35 ppt seawater.

 

[Randy Holmes-Farley]

The Hanna is showing 1.027 @ 72, the handheld thermometer is 74.5. The TM is showing 1.039, and both refractometers are showing about 1.024. The swing arm is showing about 1.025

 

[Randy Holmes-Farley]

I’m not seeing a big issue with the above observation, except the TM. All of these devices have a range of variability. If the actual value is about 1.0255, all are within or close to the expected range of error. Don’t get too caught up in exact values from any hobby devices.

On the TM, I do not know why it deviates in one solution and not the other. I’d check them all in their respective calibration solutions:

Reef Aquarium Salinity: DIY Calibration Standards

Reef Aquarium Salinity: DIY Calibration Standards By Randy Holmes-Farley One of the most important issues facing marine aquarists is providing a suitable environment for their aquaria's inhabitants. Among the important properties for a marine...

www.reef2reef.com

 

[aSaltyKlown]

Thanks Randy, appreciate the feedback. I plan on making the solution once I get the grad cylinder on Sat. as I don't have anything else to put the TM in without making gallons.

If I didn't have the TM, I'd not be as skeptical and go forward with the current test results, or if I only had the TM for that matter.

 

[Randy Holmes-Farley]

One thing that can be done to check the temp correction ability of any device is take warm tank water, measure it, then put it in a cool place, let that same sample cool, and measure salinity as it cools. Perfect values will be unchanged.

 

[RelaxingWithTheReef]

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.

This is the test result of my Hanna tester and calibration packet. Your tester and calibration packet are likely different. But I hope this helps in understanding the Hanna tester a little better.