Help me understand Hanna Checker Salinity changes with temperature

[Frogspon]

When I put the hanna checker into the tank water at 79 degrees, I get a reading of 1.024

When that same water comes down to room temp, and I check again, it reads between 1.027-1.028 (which is verified with two separate calibrated refractometers)

I'm not sure what my tank SG actually is....

What do I need to know here to accurately measure the SG of my tank at it's normal running temp?

Thanks.

 

[TeamTurtle]

As water evaporats and cools your tank, your salinity goes up. Water leaves and salt stays. This is when you need to top off your tank with fresh water.

 

[TeamTurtle]

I would also check the calibration of your hanna checker with their calibration sache if you have not already. But the difference in the salinity level is almost always do to evaporation.

 

[Deep]

When I put the hanna checker into the tank water at 79 degrees, I get a reading of 1.024

When that same water comes down to room temp, and I check again, it reads between 1.027-1.028 (which is verified with two separate calibrated refractometers)

I'm not sure what my tank SG actually is....

What do I need to know here to accurately measure the SG of my tank at it's normal running temp?

Thanks.

1.026 or 1.023 etc is Specific Gravity which can vary like you said based on temperature. this is not a direct measure of salinity. Specific gravity can change based on density of water ( water is more dense at lower temperatures for the same amount of salt).
But salinity on the other hand should be constant across temperature and is measured in ppt ( usually 35 ppt).

At 26.1 degree celcius if you measure specific gravity at 1.025, then the salinity of the water is 35.6 ppt.

 

[homer1475]

Refractometers measure density which can change with anything in the water. This can also change with temperature, which is why most refractometers come with ATC(Automatic temperature compensation). @Randy Holmes-Farley has a paper somewhere(I'm sure you can google it) that gives the table for salinity at different temperatures.

The Hanna measures in conductivity which only changes when the salt level changes.

Guess which one is used by scientists to measure the salinity of salt water?

 

[Frogspon]

Refractometers measure density which can change with anything in the water. This can also change with temperature, which is why most refractometers come with ATC(Automatic temperature compensation). @Randy Holmes-Farley has a paper somewhere(I'm sure you can google it) that gives the table for salinity at different temperatures.

The Hanna measures in conductivity which only changes when the salt level changes.

Guess which one is used by scientists to measure the salinity of salt water?

Then why does the Salinity change in real time on my Hanna Checker as the temperate is adjusted? The Salinity goes down as the Temp is going up.

Also, if I take a cup of my tank water and set it out to cool down (with a lid/no evap), it will read higher than the tank when cool..

I've also noticed the checker thinks everything is 80 degrees plus, regardless of what all my other equipment says. i/e I put three thermometers and a heater in a bucket. The heater is at 78, the thermometers read 78, the hanna checker reads 80.4.....

I'm beginning to think the checker is faulty.

 

[Deep]

Then why does the Salinity change in real time on my Hanna Checker as the temperate is adjusted? The Salinity goes down as the Temp is going up.

Also, if I take a cup of my tank water and set it out to cool down (with a lid/no evap), it will read higher than the tank when cool..

I've also noticed the checker thinks everything is 80 degrees plus, regardless of what all my other equipment says. i/e I put three thermometers and a heater in a bucket. The heater is at 78, the thermometers read 78, the hanna checker reads 80.4.....

I'm beginning to think the checker is faulty.

I have already answered that above. Your salinity is not changing, your specific gravity is changing.

 

[Randy Holmes-Farley]

I have already answered that above. Your salinity is not changing, your specific gravity is changing.

I do not think that is really true (specific gravity barely changes at all with temperature), and is not the explanation.

 

[Randy Holmes-Farley]

Conductivity changes with temperature, and conductivity devices are supposed to account for that change. It appears the Hanna is not doing that correctly.

 

[Randy Holmes-Farley]

I discuss various attributes of measuring salinity by conductivity here:

AquariumFish.com :: Aquarium Fish International :: The monthly magazine for both novice and expert aquarium hobbyists.

AQUARIUM FISH MAGAZINE is THE monthly magazine for both novice and expert aquarium hobbyists. Aquarium Fish Magazine provides information on choosing, caring for, and breeding freshwater and marine fish.

web.archive.org

from it:

One final complication is that the conductivity of ions in water depends upon temperature. There are a number of factors that cause this in seawater, but one big one is simply that the ions are naturally moving around faster as they get warmer. When the same number of ions are moving faster, the apparent conductivity is increased. The conductivity of seawater at 41 degrees Fahrenheit, for example, is a little over half of that at 56 degrees. For this reason, all conductivity meters simultaneously measure the conductivity and the temperature. The internal electronics then take the temperature into account, and normally provide a value that is “corrected” to what the conductivity would be at a standard temperature (47 degrees). Consequently, you can measure the salinity of water regardless of the temperature of the sample.

The exact dependence of the conductivity of seawater on temperature is well known, and some meters use this exact relationship. Other use a slightly different correction — that for simple aqueous solutions. Still others provide several temperature correction options. The closer that you are to 47 degrees, the smaller the correction is and the less important the nature of the correction used. Nevertheless, if you have a choice, select the correction used for seawater. If you don’t, you won’t be far off.

 

[Deep]

I do not think that is really true (specific gravity barely changes at all with temperature), and is not the explanation.

thanks Randy, I am sure you already know all this..

"Specific gravity is the density of an object or liquid in comparison to the density of water at an exact temperature and an exact pressure. Changes in temperature and pressure effect the density of objects and liquids and therefore effect the specific gravity of objects and liquids."

 

[infinite0180]

My hanna will read the same conductivity in ppt regardless of temp...

edit to clarify. I have mine set to ppt mode. I can check my tank water and get 35.1. If i remove a cup of tank water and place the checker in it and walk away for 20 min and come back it will still show very close to 35.1 if not still 35.1 on the dot. The temp reading will be lower obviously. If the meter is not correcting for temp then its broken. Also dont use hannas calibration packets. Randy explains how to make a diy conductivity solution in an article that has been a life saver for me...

 

[Deep]

My hanna will read the same conductivity in ppt regardless of temp...

mine reads sg not ppt and it changes with temperature.

 

[Deep]

My hanna will read the same conductivity in ppt regardless of temp...

edit to clarify. I have mine set to ppt mode. I can check my tank water and get 35.1. If i remove a cup of tank water and place the checker in it and walk away for 20 min and come back it will still show very close to 35.1 if not still 35.1 on the dot. The temp reading will be lower obviously. If the meter is not correcting for temp then its broken. Also dont use hannas calibration packets. Randy explains how to make a diy conductivity solution in an article that has been a life saver for me...

If you change that to read that set to read SG instead of ppt you will experience what the OP is complaining about,.

 

[infinite0180]

If you change that to read that set to read SG instead of ppt you will experience what the OP is complaining about,.

Yea im not really sure why anybody would buy a conductivity tester and have it read in SG. If i wanted SG i would use a refractometer. I dont understand why anybody would use SG over conductivity, as a method for salinity testing.

 

[Deep]

Yea im not really sure why anybody would buy a conductivity tester and have it read in SG. If i wanted SG i would use a refractometer. I dont understand why anybody would use SG over conductivity, as a method for salinity testing.

because thats the default out of the box for the hanna ? And the fact that to change it is hidden inside the battery compartment and is difficult to find ?

 

[infinite0180]

because thats the default out of the box for the hanna ? And the fact that to change it is hidden inside the battery compartment and is difficult to find ?

Most testing equipment requires some form of set up and calibration...

i will change mine to SG and confirm its behavior.

 

[Randy Holmes-Farley]

thanks Randy, I am sure you already know all this..

"Specific gravity is the density of an object or liquid in comparison to the density of water at an exact temperature and an exact pressure. Changes in temperature and pressure effect the density of objects and liquids and therefore effect the specific gravity of objects and liquids."

In actual fact, the specific gravity of seawater by that definition has only a miniscule change with temperature. That is because seawater and the comparator fresh water change density in an almost identical fashion.

 

[Randy Holmes-Farley]

Example:

Chemistry and the Aquarium: Specific Gravity: Oh How Complicated!

This month, Randy explains and reviews specific gravity.

reefs.com

The specific gravity of natural seawater (S =35) is

1.0278 at 3.98 °C ,
1.0269 at 60 °F
1.0266 at 20 °C,
1.0264 at 77 °F.

Unless you are talking about big temp swings, the sg is nearly unchanged.

 

[Deep]

Example:

Chemistry and the Aquarium: Specific Gravity: Oh How Complicated!

This month, Randy explains and reviews specific gravity.

reefs.com

The specific gravity of natural seawater (S =35) is

1.0278 at 3.98 °C ,
1.0269 at 60 °F
1.0266 at 20 °C,
1.0264 at 77 °F.

Unless you are talking about big temp swings, the sg is nearly unchanged.

I think we are talking about 2-3 deg c. and you should see a difference in sg ?

at 24.5 the sg is 1.025 ( S=35)
at 27.8 the sg is 1.024 (S=35)

thats also the behaviour that the OP is seeing.