Salinity convertion - confused on numbers.

[kilnakorr]

I did some cleaning and calibration on my salinity/conductivity probe yesterday, and did some reading on the various numbers that my GHL shows. Using some online convertion calculators, things don't really add up.

The GHL shows these numbers:
1.0225 kg/L
49,3 ms/cm
32,5 PSU

Converting these numbers to SG:

1,0255 sg
1,0243 sg
1,0245 sg

Am I missing something here, or are the GHL convertions incorrect?

 

[Lasse]

or are the GHL convertions incorrect?

At least - it is different - please see here

Conductivity-Salinity calculators vs. ProfiLux calculated values

www.aquariumcomputer.com

Sincerely Lasse

 

[kilnakorr]

At least - it is different - please see here

Conductivity-Salinity calculators vs. ProfiLux calculated values

www.aquariumcomputer.com

Sincerely Lasse

Thanks for the link.
What puzzles me is the convertion that GHL makes does not add up:
Using ms/cm it shows : 49,3 which equals 1,0212 kg/L.
So why does it show 1.0223 when using this reading?
With this difference the measurements are so far apart, that it is completely useless.

 

[Lasse]

49,3 which equals 1,0212 kg/L

According to what?

Sincerely Lasse

 

[kilnakorr]

According to what?

Sincerely Lasse

I've used 3 different online calculators.
They all give same results eg.:

Oceanlife - Water Salinity Converter en

Oceanlife Water Salinity Converter - Software per la conversione dei parametri fondamentali dell'acqua marina

www.oceanlife.it

 

[arking_mark]

GHL is doing several non-standard things with their salinity measurements.

Issue with GHL salinity measurements

Simply stated, the salinity measurements of this device is inconsistent with itself! I have a measured GHL salinity at 53ms/cm, 34.7psu, 1.0246 @ 76.9 degrees. Per reef calculators, 53ms/cm = 35ppt (35psu) and 1.0234 kg/l (1.0264 sg) Why would this be the case? Which is right? Is this a bug?

www.reef2reef.com

Here is what I concluded...

Salinity Measurement Troubles...

So I've been dealing with a couple of meters that all give me different readings after being calibrated: GHL = 34.6 psu, 52.7mS, 1.0245kg/l Hanna = 35.4ppt Other probe = 37.3ppt I bought a Tropic Marin Precision Hydrometer to establish ground truth... Tropic Marin Precision Hydrometer: 1.02775...

www.reef2reef.com

 

[kilnakorr]

GHL is doing several non-standard things with their salinity measurements.

Issue with GHL salinity measurements

Simply stated, the salinity measurements of this device is inconsistent with itself! I have a measured GHL salinity at 53ms/cm, 34.7psu, 1.0246 @ 76.9 degrees. Per reef calculators, 53ms/cm = 35ppt (35psu) and 1.0234 kg/l (1.0264 sg) Why would this be the case? Which is right? Is this a bug?

www.reef2reef.com

Here is what I concluded...

Salinity Measurement Troubles...

So I've been dealing with a couple of meters that all give me different readings after being calibrated: GHL = 34.6 psu, 52.7mS, 1.0245kg/l Hanna = 35.4ppt Other probe = 37.3ppt I bought a Tropic Marin Precision Hydrometer to establish ground truth... Tropic Marin Precision Hydrometer: 1.02775...

www.reef2reef.com

Thank you.
So it seems GHL numbers really doesn't line up, but the density measurement in kg/L is farly accurate?

 

[Lasse]

Use the density offset there you can adapt your water reading to standar kg/L

Example from my salinity meter

Close enough IMO

However - IME - sometimes the probes do not (in PSU) match my refractometer. In these cases - I calibrate my refractometer with a standard for refractometers and switch to manual temperature compensation. In my last case - I have that at 23.6- I can do this because my temperature is very stable

Sincerely Lasse

 

[kilnakorr]

Use the density offset there you can adapt your water reading to standar kg/L

Example from my salinity meter

Close enough IMO

However - IME - sometimes the probes do not (in PSU) match my refractometer. In these cases - I calibrate my refractometer with a standard for refractometers and switch to manual temperature compensation. In my last case - I have that at 23.6- I can do this because my temperature is very stable

Sincerely Lasse

I am unsure what you mean with the offset.
I'm not looking at the control center but the app, which shows a more precise density.
Right now I'm looking at 1.0227 kg/L, which should be the same as 51.92 mS/cm.
However, when showing this number in mS/cm I have 49.5.

Just like temperature can be shown in c and f, I have 25 C and changing to F it should show 77 as this is the same temperature. It it was to show 84F instead then clearly something is wrong.

 

[Lasse]

Play with this figure - you can change ± 0.005

49.5 is your measured, real value. Because of different way to calculate you need to set an offset that show your calculated density. According to your own link - 49.5 correspond to 1.021, If you put in -0.001 you will be close enough

It is not the same as C and F conversions - that conversion is a linear conversion not linked to any else factor as salinity in kg/L. If the conductivity that you measure is caused of heavy ions - you will get another salinity in kg/L compared if the same conductivity depends on light ions. The conductivity of a water depends on the amount of ions - the salinity in Kg/L depends of the weight of these ions

Sincerely Lasse

 

[kilnakorr]

Play with this figure - you can change ± 0.005

Sincerely Lasse

I get that, but why?
I'm simply wondering why to different units are showing different salinity.

 

[Lasse]

I get that, but why?
I'm simply wondering why to different units are showing different salinity.

See my edit above. Conductivity - amount of ions, salinity in kg/L - the weight of these ions.

Conductivity is the ability of a water to transport electricity (ledningsförmåga på svenska - ledningsevne på dansk) It is not salinity. Salinity is either the weight of the salts in the water or the percent of the weight of 1 L water (ppt (promille på dansk) or the corrected PSU - practical salinity unit

Sincerely Lasse

 

[kilnakorr]

See my edit above. Conductivity - amount of ions, salinity in kg/L - the weight of these ions.

Conductivity is the ability of a water to transport electricity (ledningsförmåga på svenska - ledningsevne på dansk) It is not salinity. Salinity is either the weight of the salts in the water or the percent of the weight of 1 L water (ppt (promille på dansk) or the corrected PSU - practical salinity unit

Sincerely Lasse

Yes, I know.
But why do these convertions even exists if it isn't possible?
If a probe is to meant to give me an idea of the salinity, then showing different values of salinity based on the readings does not make any sense.

 

[Lasse]

Once again - conductivity is not a direct measurement of salinity. Its a method to measure a proximity of salinity - you need to have a conversion method if you want it expressed it as salinity.

Sincerely Lasse

 

[kilnakorr]

Once again - conductivity is not a direct measurement of salinity. Its a method to measure a proximity of salinity - you need to have a conversion method if you want it expressed it as salinity.

Sincerely Lasse

Yes, I get that.
My real life provlem/confusement is this:

49.6 ms/cm = 32.6 ppt
1.0227 kg/l = 34.1 ppt

So my converted salinity is not the same, depending on how I chose to see the readings.
It might be because of ions etc. but it just shows these readings can not be even remotely trusted for salinity, and makes this function of the GHL useless.

 

[arking_mark]

Thank you.
So it seems GHL numbers really doesn't line up, but the density measurement in kg/L is farly accurate?

That's what lined up for me...

 

[kilnakorr]

That's what lined up for me...

It seems so. The density matches my refractometer, but the PSU and ms/cm value is much lower.

 

[Lasse]

My real life provlem/confusement is this:

49.6 ms/cm = 32.6 ppt
1.0227 kg/l = 34.1 ppt

I do not understand where the problem is. If you use the correction -0.0013 for the real value of 49.6 and express this in kg/l you get 1.0214 and 32.5 psu.

If you do the same in your conversion table (49,6) you get as below - 32.4 psu and 1021.41 g/L around 1.0214 kg/L

49.5 is your measured value. To get the right density according to to the conversion tool you need to use the offset of -0.0013 - you real kg/L is 1.0214. Thats correspond to 32.5 psu in GHL - enough close to 32.4 in your table

Sincerely Lasse

 

[Lasse]

The density matches my refractometer

Your refractometer show the relative density - it is not the same density expressed as kg/L

Sincerely Lasse

 

[kilnakorr]

I do not understand where the problem is. If you use the correction -0.0013 for the real value of 49.6 and express this in kg/l you get 1.0214 and 32.5 psu.

If you do the same in your conversion table (49,6) you get as below - 32.4 psu and 1021.41 g/L around 1.0214 kg/L

49.5 is your measured value. To get the right density according to to the conversion tool you need to use the offset of -0.0013 - you real kg/L is 1.0214. Thats correspond to 32.5 psu in GHL - enough close to 32.4 in your table

Sincerely Lasse

That much I get.
Would this mean that these values are not the measurements?
If this is true, why is the kg/L without offset closer to other readings (refractometer, my handheld conductivity device, and the devices @arking_mark has used)?
It seems the 49.5 ms/cm is incorrect, and should be offset according to the density value.