Kessil

Salt mixing temperature

[mention]JVU [/mention] I was not trying to disprove your statement by posting the Apex screenshot. I get what you’re saying and appreciate your graciousness.
 
Key:
True salinity does NOT change with temperature.
But almost all MEASUREMENTS do change if not properly compensated.

Salinity is based on grams of salt dissolved in a kilogram of water.
Temperature does not affect mass, so that ratio cannot change with temperature.

Unfortunately measurements (conductivity and refractivity) are actually based on density, since it is obviously very hard to measure the different masses.
Temperature does affect density since the water expands.
Hence, the real salinity does not change, but it looks like it does.
 
rygh said:
Salinity is based on grams of salt dissolved in a kilogram of water.
Temperature does not affect mass, so that ratio cannot change with temperature.

Unfortunately measurements (conductivity and refractivity) are actually based on density, since it is obviously very hard to measure the different masses.
Temperature does affect density since the water expands.
Hence, the real salinity does not change, but it looks like it does.
Click to expand...
Well I really want to poke a bear right now... (better than saying I want to stir something up :D)

But volume is dependent on density, so the amount of salt that we add to a fixed volume of water will be different mass based on the temperature. So the salinty we are making would change based on temperature. a 5 gallon bucket of water at 50° weighs different than a 5 gallon bucket at 80° because they have different masses :D

Ok, that's my one cabin fever moment of the day :D
 
sfsuphysics said:
Well I really want to poke a bear right now... (better than saying I want to stir something up :D)

But volume is dependent on density, so the amount of salt that we add to a fixed volume of water will be different mass based on the temperature. So the salinty we are making would change based on temperature. a 5 gallon bucket of water at 50° weighs different than a 5 gallon bucket at 80° because they have different masses :D

Ok, that's my one cabin fever moment of the day :D
Click to expand...

Sure, but temperature can also affect humidity, which may affect the amount of moisture that may be in the salt mix, affecting the mass of what you mix in,
and blah blah blah.
:)


I do want to emphasize for everyone: If you sea a salinity measurement changing with temperature, it is WRONG.
Yes, that Apex is WRONG. Simple as that. (Note that there is a setting in the apex for temp compensation)
True salinity is mass based, and thus cannot really change on temperature.
 
JVU said:
I’m sorry I wasn’t clear enough and you both missed the point I was trying to make twice. But I have no interest in being argumentative or repeating myself, so just carry on. There are many paths to success in this hobby.
Click to expand...
John it's not argument its discussion for the sake of learning. Please do correct us if you see a wrong statement. Am learning as I go.
Thanks
 
rygh said:
Sure, but temperature can also affect humidity, which may affect the amount of moisture that may be in the salt mix, affecting the mass of what you mix in,
and blah blah blah.
:)


I do want to emphasize for everyone: If you sea a salinity measurement changing with temperature, it is WRONG.
Yes, that Apex is WRONG. Simple as that. (Note that there is a setting in the apex for temp compensation)
True salinity is mass based, and thus cannot really change on temperature.
Click to expand...
Am confused about the last paragraph. Are we saying temp do not impact salinity? I saw couple of tech papers link temp to density, and density to salinity. The papers say when temp change it change density which change salinity. That's what happening in the oceans now with global warming..is this understanding incorrect?
Appreciate the input.
 
rygh said:
Sure, but temperature can also affect humidity, which may affect the amount of moisture that may be in the salt mix, affecting the mass of what you mix in,
and blah blah blah.
:)
Click to expand...
Hey I said ONE cabin fever moment of the day, you have to wait until tomorrow to post something new for me to respond :D
 
ofzakaria said:
Am confused about the last paragraph. Are we saying temp do not impact salinity? I saw couple of tech papers link temp to density, and density to salinity. The papers say when temp change it change density which change salinity. That's what happening in the oceans now with global warming..is this understanding incorrect?
Appreciate the input.
Click to expand...

So "climate change" is truly affecting the oceans salinity.
Various ratios and number of ions is changing due to various climate change processes.
But it is not directly due to density only. It is more about ocean chemistry changing.

Raw uncompensated PSU and mS/cm2 do change, and that is what people usually talk about and use in tables and graphs.
So my guess is that most of the papers you see are doing that.
I would not call it wrong. Just a bit sloppy at most.

If a paper directly states that salinity changes on density, it is wrong.

Think about the endless confusion between mass and weight.
 
rygh said:
So "climate change" is truly affecting the oceans salinity.
Various ratios and number of ions is changing due to various climate change processes.
But it is not directly due to density only. It is more about ocean chemistry changing.

Raw uncompensated PSU and mS/cm2 do change, and that is what people usually talk about and use in tables and graphs.
So my guess is that most of the papers you see are doing that.
I would not call it wrong. Just a bit sloppy at most.

If a paper directly states that salinity changes on density, it is wrong.

Think about the endless confusion between mass and weight.
Click to expand...
That's great input. Thank you.
So are we saying that when salinity of the same water sample change when its temperature change is due to the measurment method?
 
ofzakaria said:
In your opinion what's the best way to get the target salinity measurment during mixing?
Sorry for the 21 question ha ha..
Click to expand...
Refractometers have temperature compensation in them.
To maximize accuracy, make sure to calibrate and measure in the same place/temp as you store the device.

So as long as you test/adjust, you should be fine.

Just do not trust Apex.
 
rygh said:
Refractometers have temperature compensation in them.
To maximize accuracy, make sure to calibrate and measure in the same place/temp as you store the device.

So as long as you test/adjust, you should be fine.

Just do not trust Apex.
Click to expand...
You are awesome thank you for all this info and explanation!
I trust refractometers the most but I feel I need to be extra careful with calibration procedure. As you said I care alot about the calibration solution temp, the water mix temp and the refracto temp when I do the measurment to have relatively similar conditions between call solution and the water mix..
Then I use the digital refracto for spot check and or frequent tank water checks..
Thanks again.
 
JVU said:
Salinity doesn’t change with temperature. But your reading could if you are testing water that is a different temp from that with which you calibrated. If you calibrate at room temp, and then just let the sample warm up to room temp you will get an accurate reading.
Click to expand...
 
(Not disagreeing with anyone - just saying it out loud for clarification after some research)

So, true salinity is a mass measurement, which is not affected by temperature. Seawater has a salinity of 35 ppt.

Conductivity (Apex) and refraction measurements are affected by temperature because they are density based and only a proxy for true salinity.

The only way to measure true salinity is to boil the salt out of the water and divide it’s weight by the weight of the water. This will be the same no matter the temp.
 
I think about it this way. 35 ppt means you have 35 parts of salt for every 1000 parts of water (you could also say it’s 3.5%). So if I take 1000 cups of water and 35 cups of salt and mix them together it will be 35 ppt. Adding or taking away water or salt from the tank will change this since it will no longer be 35 parts salt to 1000 parts water but temperature has no bearing on the ratio.
 
Flagg37 said:
I think about it this way. 35 ppt means you have 35 parts of salt for every 1000 parts of water (you could also say it’s 3.5%). So if I take 1000 cups of water and 35 cups of salt and mix them together it will be 35 ppt. Adding or taking away water or salt from the tank will change this since it will no longer be 35 parts salt to 1000 parts water but temperature has no bearing on the ratio.
Click to expand...
Great analogy:)
 
Flagg37 said:
I think about it this way. 35 ppt means you have 35 parts of salt for every 1000 parts of water (you could also say it’s 3.5%). So if I take 1000 cups of water and 35 cups of salt and mix them together it will be 35 ppt. Adding or taking away water or salt from the tank will change this since it will no longer be 35 parts salt to 1000 parts water but temperature has no bearing on the ratio.
Click to expand...
No, because cups are VOLUME, and the grams of water per cup will vary by temperature due to expansion and change in density.

The only way to avoid temperature issues is by carefully weighing salt and water.
Since that is impractical, your next bet is to measure it with a temperature calibrated device and adjust.
 
rygh said:
No, because cups are VOLUME, and the grams of water per cup will vary by temperature due to expansion and change in density.

The only way to avoid temperature issues is by carefully weighing salt and water.
Since that is impractical, your next bet is to measure it with a temperature calibrated device and adjust.
Click to expand...
Man the more I read here and outside the forum, look like the best way to avoid issues are:
1- as you said weigh in the salt to be used if you know how much would make the salinity you looking for
2- eliminate temp factor by trying our best to have all conditions within similar or close temp to your system temp.
3- if we are depending on refracto to reach the salinity we want by adding cups of salt to rodi, we should try to have the cal solution similar temp to the refracto and the rodi water so measurments during calibration and during testing the water mix are within close proximity so the atc take care of other compensation..

@rygh do you see a hole in the above?
 
Last edited:
You must log in or register to reply here.
Back
Top