Confirming Salinity Between Tools - Hanna Salinity Tester

Slider162 · Mar 30, 2026

I like the Hanna because of the convenience and ease of use. But right now, it has me questioning the salinity in my new tank using Instant Ocean.

I have:

A Salinity Refractometer (New)
A Calibrated Neptune Apex Probe (Old)
A Calibrated Hanna Salinity Tester (New)

I'm on my second Hanna Salinity Tester because the first was exchanged for the same issue. The replacement is identical to the first.

The refractometer and Neptune probe have always agreed with each other.

Right now:

Neptune = 34.2ppt
Refractometer = 1.025
Hanna = 29.8ppt

Then I read the Reef Aquarium Salinity: Homemade Calibration Standards and dissolved 6.2g of table salt with 182ml RODI. Everything matched. Neptune was at 35ppt, Hanna was ballpark 34.4ppt, and refractometer was just a hair above 1.025.

So why would the Hanna Salinity Tester read so low in aquarium water?

Randy Holmes-Farley · Mar 31, 2026

Just an fyi, those devices will not perfectly match in a single diy fluid. There are different recipes for different types of devices. You are using all three different types.

That does not explain your issue with the Hanna, however. It also is not necessarily the Hanna that is off.

Try measuring the conductivity meter standard and the tank water in a cup at the same room temperature using the Hanna.

exnisstech · Mar 31, 2026

I've had two Hanna salinity checker's and both would read 0.002 low when calibrated using Hanna calibration solution. They were compared to TM hydrometers and refractometer calibrated with Randy's solution. Mine would also drift so I scrapped them. From reading it seems its not an uncommon issue having the Hanna read low.

Randy Holmes-Farley · Mar 31, 2026

That experience is common and why I suspect the issue may be the fault of the Hanna solution not being correct.

Slider162 · Mar 31, 2026

Out of curiosity, I calibrated the Hanna with the home made solution and the results were not any better. Aquarium water is still 4-5ppt low on the Hanna.

exnisstech · Mar 31, 2026

My Hannas are in the landfill. I didn't trust them so I wasn't comfortable selling something I would not use myself.

Slider162 · Mar 31, 2026

It hasn't been 30 days, so I'm asking to exchange for a Milwaukee. Hate to see someone starting out and only using the Hanna. I posted here because I needed a sanity check.

W31Olds · Mar 31, 2026

I would measure some newly mixed SW. Hanna is a conductivity meter so I would image it could be affected by particulates and metals in the Water.

Randy Holmes-Farley · Mar 31, 2026

Slider162 said:
Out of curiosity, I calibrated the Hanna with the home made solution and the results were not any better. Aquarium water is still 4-5ppt low on the Hanna.

Did it read the standard correctly after calibration? Was the temp the same?

I just do not understand how a conductivity meter can read two solutions with the same conductivity at the same temperature differently.

Randy Holmes-Farley · Mar 31, 2026

W31Olds said:
I would measure some newly mixed SW. Hanna is a conductivity meter so I would image it could be affected by particulates and metals in the Water.

No, that is not the issue. Metals are conductive ions, but at very low concentration and nonconductive particulates are mostly ignored by conductivity meters unless there are so many that they occupy a significant fraction of the water volume (and they do not in new seawater, even if cloudy.

Slider162 · Mar 31, 2026

I actually use the Hanna to mix my water. I just mix it at 30ppt and it shows up in my tank on the Neptune as 34-35ppt.

The standard reads 38.4 after calibrating in the home brew. Both have been sitting at room temp overnight since I started this thread.

After calibrating again with the standard and dipping in the home brew this morning is 31.9ppt. Tank now reads 28.0ppt.

Tank is 9.2F warmer than room temp solutions. But if we believe the marketing, the Hanna is supposed to be temperature compensated.

Randy Holmes-Farley · Mar 31, 2026

Well that is strange. Why would the 35 ppt standard not read 35 ppt after calibration with it?

I don’t know how the electronics of the Hanna calibrates. Does it let you tell it what the salinity is when calibrating?

Slider162 · Mar 31, 2026

Maybe I misread the question. After calibrating with the standard, the standard tests at 34.4ppt.

NanoSteam · Mar 31, 2026

Randy Holmes-Farley said:
Did it read the standard correctly after calibration? Was the temp the same?

I just do not understand how a conductivity meter can read two solutions with the same conductivity at the same temperature differently.

Mine also had issues with temperature correction... It read anywhere from 2 to 4 degrees F low so I wonder if that's also causing some issues.

Two tanks with 3 different thermometers including a standard glass thermometer that match but Hannah would be 2 to 4 degrees lower with no explanation.

Randy Holmes-Farley · Mar 31, 2026

Slider162 said:
Maybe I misread the question. After calibrating with the standard, the standard tests at 34.4ppt.

Ok, still strange it not as much so. Do you tell it the standard is 35 ppt? It’s almost as if the standardization process did not actually change the meter.

Randy Holmes-Farley · Mar 31, 2026

NanoSteam said:
Mine also had issues with temperature correction... It read anywhere from 2 to 4 degrees F low so I wonder if that's also causing some issues.

Two tanks with 3 different thermometers including a standard glass thermometer that match but Hannah would be 2 to 4 degrees lower with no explanation.

Maybe. I think it should not matter if it also reads the standard low, unless it electronically requires a specific temp for the standard.

The correction is a fixed change in conductivity vs degree F (or C).

NanoSteam · Mar 31, 2026

Randy Holmes-Farley said:
Maybe. I think it should not matter if it also reads the standard low, unless it electronically requires a specific temp for the standard.

The correction is a fixed change in conductivity vs degree F (or C).

Well in my case it didn't read the standard low... that was fine but putting it in the tank that's verified at 78F and it reads 74F is problematic I'd think. If I open a fresh solution packet it'll read 35ppt.

This is with tank salinity verified through calibrated refractometer that agrees with the TM glass hydrometer.

Randy Holmes-Farley · Mar 31, 2026

NanoSteam said:
Well in my case it didn't read the standard low... that was fine but putting it in the tank that's verified at 78F and it reads 74F is problematic I'd think. If I open a fresh solution packet it'll read 35ppt.

This is with tank salinity verified through calibrated refractometer that agrees with the TM glass hydrometer.

Temperature correction for a conductivity meter should only be an issue if it sometimes corrects and sometimes not (like a reading vs standardization). If it just always read temps 4 degrees too low, that would not cause an issue. The temperature correction of the standard and the sample is the same.

But it is prudent to have the standard and tank sample at the same temp and close to 25 deg C if you think there may be a temp correction issue.

Mandarinkeeper · Mar 31, 2026

Why not use the TM hydrometer as the reference and calibrate to a known dependable instrument that isn’t influenced by calibration fluids of unknown accuracy. J

Randy Holmes-Farley · Mar 31, 2026

Mandarinkeeper said:
Why not use the TM hydrometer as the reference and calibrate to a known dependable instrument that isn’t influenced by calibration fluids of unknown accuracy. J

You assume it is accurate. I would not assume it is accurate without testing it against a fluid of known density. There are high quality seawater standards used by labs. Reefers just like to cheap out.

I’d have a lot more confidence in a standard I made using a calibrated scale than an inexpensive and untested hydrometer in which the paper may have slipped, the guy making it got a text at the wrong moment, etc.

Once validated with a test, I agree that is a good way to check other equipment.