Salinity

[rusty dowell]

Whether I’m using a hydrometer or refractometer or Hannah
I try to maintain 1.026

If you measure the water at 78° is 1.026
Room temp 70 1.027

Here’s the question at what temp are we measuring the salinity of our water?

 

[Randy Holmes-Farley Verified Community Expert]

Whether I’m using a hydrometer or refractometer or Hannah
I try to maintain 1.026

If you measure the water at 78° is 1.026
Room temp 70 1.027

Here’s the question at what temp are we measuring the salinity of our water?

For reasonable temp changes like you suggest, you only need to think carefully about temp when using a glass hydrometer. Plastic swing arm types and other methods we use self correct for the temp effects they experience. The Hanna does, as does any refractometer that mentions ATC.

There are tables for correcting glass hydrometer readings, but the hydrometer should say on it what it’s calibration temp is (the temp at which it needs no correction).

Thus, asking what temp folks measure at will give answers that are not useful to you.

This is all a bit of an oversimplification, but that is true when you dig deep on most things we do.

What type of hydrometer?

 

[rusty dowell]

Glass hydrometer
Hannah salinity checker
Handheld refractometer
They’re all the same you’re getting two different measurements at two different temperatures
The question is is measured at 78° or is it measured at room temperature?

 

[Randy Holmes-Farley Verified Community Expert]

Glass hydrometer
Hannah salinity checker
Handheld refractometer
They’re all the same you’re getting two different measurements at two different temperatures
The question is is measured at 78° or is it measured at room temperature?

Again, that's the wrong question for the reason I mentioned.

Salinity does not change AT ALL with temperature.

Specific gravity changes are very small with temperature and not worth a beginner even thinking about. I can expand on the gory details of specific gravity definitions and such, but I won't do that unless you really want details that may just be confusing at this point.

Glass hydrometer readings do change a lot with temperature. That NOT because specific gravity is changing, but because that measurement tool has problems with temperature changes that it cannot self correct, and you need a table.

The Hanna and the refractometer (assuming it ATC (automatic temperature compensation), as most are in the hobby) also have issues with temperature, but they are self correcting. They can be used at other temperatures without manual correction by you.

What glass hydrometer? Brand. or does it say a temp on it? Tropic Marin hydrometers are usually calibrated for use at 77 deg F, and may say so on the paper inside of it. If you use that at other temps than 77, then use a table to correct that specific hydrometer.

https://www.tropic-marin-smartinfo.com/cylinder?lang=en

 

[Malum Argenteum]

Here’s the question at what temp are we measuring the salinity of our water?

Tank temp.

 

[rusty dowell]

Yes, glass hydrometer from Tropic Marine. The salinity increases when the temperature cools.


The Hannah checker You put it in the tank the salinity reads at a higher salinity until it measures the temperature of the water


The simple refractometer also changes when the temperature gets cooler

Are you telling me that salinity measurement doesn’t change with the temperature?

 

[KStatefan]

Here’s the question at what temp are we measuring the salinity of our water?

What ever the temperature of the water is.

 

[rusty dowell]

Correct
So we all can agree that temperature affects salinity reading
And if you keep your tank at 78°, and the temperature house is 70°
If you don’t measure the salinity of your tank at 78 you were getting an inaccurate reading

 

[KStatefan]

Correct
So we all can agree that temperature affects salinity reading
And if you keep your tank at 78°, and the temperature house is 70°
If you don’t measure the salinity of your tank at 78 you were getting an inaccurate reading

No

If I pull a sample of water from my tank at 78° F it will not be at that temperature when I measure since the hydrometer and the graduated cylinder will be at a lower temp. I let the temp stabilize the take the hydrometer reading and temperature reading then use a formula to correct the reading for not being at the temperature the hydrometer is calibrated at.

 

[Troylee]

No

If I pull a sample of water from my tank at 78° F it will not be at that temperature when I measure since the hydrometer and the graduated cylinder will be at a lower temp. I let the temp stabilize the take the hydrometer reading and temperature reading then use a formula to correct the reading for not being at the temperature the hydrometer is calibrated at.

It’s really not all that serious in my opinion lol.. I use a 12yr old instant ocean plastic hydrometer with a swing arm and it works just fine. Never had issues that I’m aware of with salinity! Now my apex probe that’s a different story! My readings are all over the place haha!

 

[rusty dowell]

Is it just me?
My salinity 1.026 at 78°
My salinity 1.27 at 70°
Using three different types of measurements

 

[ISpeakForTheSeas]

Correct
So we all can agree that temperature affects salinity reading
And if you keep your tank at 78°, and the temperature house is 70°
If you don’t measure the salinity of your tank at 78 you were getting an inaccurate reading

It impacts the reading of the salinity, but not the actual salinity, yes - as Randy was saying, though, the Hanna checker and the refractometer should automatically adjust their readings of the salinity to account for the temperature difference (so temperature shouldn't really influence the reading for these).

Only the glass hydrometer should need to be manually adjusted to account for the temperature difference.


I'm not knowledgeable on the testing and various methods involved to say why you're seeing the results influenced with the Hanna and the refractometer - hopefully someone will be able to help you there though.

 

[Randy Holmes-Farley Verified Community Expert]

Correct
So we all can agree that temperature affects salinity reading
And if you keep your tank at 78°, and the temperature house is 70°
If you don’t measure the salinity of your tank at 78 you were getting an inaccurate reading

No, hydrometer readings change.

Actual Salinity cannot ever change with temperature.

 

[Malum Argenteum]

Actual Salinity cannot ever change with temperature.

150°C?

 

[Randy Holmes-Farley Verified Community Expert]

Is it just me?
My salinity 1.026 at 78°
My salinity 1.27 at 70°
Using three different types of measurements

You appear to be not hearing what I wrote.

First, and important, 1.026 or any number that looks like that is Not salinity. It is likely specific gravity.

Second, presuming the second number should be 1.027, those are both within the known error of the measuring devices.

Finally, the hydrometer reading will properly change with temp. The other two will only change if the corrections they are performing for you are not perfect.

 

[Randy Holmes-Farley Verified Community Expert]

150°C?

Even then. lol

 

[Malum Argenteum]

Even then. lol

Would there be the same relative amount of salt in the steam as there was in the water when it was a liquid?

 

[Randy Holmes-Farley Verified Community Expert]

Would there be the same relative amount of salt in the steam as there was in the water when it was a liquid?

Since salinity is generally defined as grams salt per total weight in kg (ppt) then as long as the steam is still around, one might call the salinity unchanged. :)

 

[Malum Argenteum]

Since salinity is generally defined as grams salt per total weight in kg (ppt) then as long as the steam is still around, one might call the salinity unchanged. :)

Salinity is the amount of salt dissolved in the water. It would be an ad hoc definition that counts undissolved solids in an intentionally large sample.

It would also mean that if I made drinking water from SW with steam distillation, the salinity of that drinking water is the same as that of the SW. It would also mean that FW rivers have a high salinity (roughly equal to that of the oceans), but the salt that's in the river happens to mostly all be over there (points at the nearest ocean) right now.

I see you deleted your response to my 'tank temp' comment (about the temp of the sample on a refractometer quickly equalizing with room temp), so my pushing this nitpicky issue looks a little pedantic out of the context of the whole original thread.

 

[Randy Holmes-Farley Verified Community Expert]

Salinity is the amount of salt dissolved in the water. It would be an ad hoc definition that counts undissolved solids in an intentionally large sample.

It would also mean that if I made drinking water from SW with steam distillation, the salinity of that drinking water is the same as that of the SW. It would also mean that FW rivers have a high salinity (roughly equal to that of the oceans), but the salt that's in the river happens to mostly all be over there (points at the nearest ocean) right now.

I see you deleted your response to my 'tank temp' comment (about the temp of the sample on a refractometer quickly equalizing with room temp), so my pushing this nitpicky issue looks a little pedantic out of the context of the whole original thread.

I thought the whole high temp discussion was a joke and treated it as such. I never meant the refractometer thing to post and didn’t realize when hours later I quoted another person, it was still there.

Anyway, salt water steam is probably something we can just move on from. :)