Salinity

[Randy Holmes-Farley]

From the above discussion, we can pull out the values for specific gravity vs temp:

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 , ​

and 1.0264 at 77 °F ​

Note, however, none of the devices we use will show all of these accurately.

 

[Randy Holmes-Farley]

Yes but he said he wanted the basic answer.

ok. I just think he will again assume his hydrometer readings or other devices are showing the sg change with temp, which none are..

 

[KStatefan]

The difference between 1.026 and 1.027 isn’t a little
Not in my opinion

And I gave you screen shots of a online calculator to correct the reading for your hydrometer since it is calibrated at 77°F and does not read correct at other temperatures.

If you do not want to use the online calculator this is the formula I use in my tracking spreadsheet.

E2* ((1.00130346 - (0.000134722124 * F2) + (0.00000204052596 * F2^2) - (0.00000000232820948 * F2^3)) / (1.00130346 - (0.000134722124 * 77) + (0.00000204052596 * 77^2) - (0.00000000232820948 * 77^3)))

E2=My hydrometer reading
F2=Temperature of the sample water in °F

I do not know what you are looking for.

 

[rusty dowell]

I do really appreciate everyone’s help.
So I guess if I would’ve readdressed the question appropriately

You do understand that’s equivalent to saying the price of gold has not changed in two years. Just a unit of measurement has changed.

 

[Randy Holmes-Farley]

I do really appreciate everyone’s help.
So I guess if I would’ve readdressed the question appropriately

You do understand that’s equivalent to saying the price of gold has not changed in two years. Just a unit of measurement has changed.

no, that is not equivalent. The change in real specific gravity with temp has absolutely nothing to do with the changes you see with any of your devices.

 

[EricR]

Still trying to understand the intent of the OP.
Not sure if either of these is close but...

Are you (OP) trying to:
1. Check new saltwater mix at room temp with a non-ATC device (floating hydrometer)?
2. Understand why a non-ATC device reads incorrect SG at temperature that's different from its calibration?

 

[ISpeakForTheSeas]

I do really appreciate everyone’s help.
So I guess if I would’ve readdressed the question appropriately

You do understand that’s equivalent to saying the price of gold has not changed in two years. Just a unit of measurement has changed.

What Randy is saying is that the salinity is the amount of dissolved salt in the water - the actual amount of dissolved salt in your water doesn't change with the temperature, but the amount of it detected by the tool used to measure it may change slightly with temperature.


So, to stick with the gold analogy:

The amount of gold on Earth doesn't change with time, but the value of gold may.

The amount of salt in the water doesn't change with temperature, but the accuracy of the tool measuring it may.



Also, another part of what Randy was getting at is that the tools we use aren't perfectly accurate to begin with - they always have some range of possible variation.

For example, with the Tropic Marin High Precision Hydrometer (a glass hydrometer that's popular in the hobby), they list their maximum deviation at 77F as 0.001 - so, if your tank water reads 1.026 with the hydrometer at 77F, then the actual specific gravity of the tank (which is technically different that salinity, but most of us in the hobby use the terms interchangeably; sorry Randy) could be as low as 1.025 or as high as 1.027.

The actual amount of variation could potentially change slightly with temperature, though, so to really highlight this variation:

Assuming your hydrometer only reads four digits (i.e. 1.026, rather than 1.0261) and assuming that it has a maximum variation of 0.0011 at 70F (assumed strictly for the sake of showing a variation exaggerated by the temperature difference), then the actual specific gravity of the tank could be 1.0265 and the tool's measurement (rounding to the nearest thousandth/third decimal place, which I personally wouldn't recommend doing with a hydrometer) could show anything from 1.025 to 1.028.


So, you could see quite a bit of variation (even with the actual amount of salt not changing at all) with the same tool even at the 77F, and it could be slightly exaggerated by using the tool at 70F.

As mentioned, though, 1.027 at 70F temp corrected to 77F reads 1.0261 - so even if your hydrometer had that variation of 0.0011, your salinity would still be between 1.025 and 1.0272; both of those numbers would generally be perfectly fine for marine organisms.


So, as long as your temperature-corrected hydrometer reads between 1.025 and 1.027, your salinity should stay in levels acceptable for marine organisms, even with any potential variation of the hydrometer itself.

 

[rusty dowell]

This thread is really going sideways
But I can share you 100% gold value has not changed the unit of measurement has changed

 

[Randy Holmes-Farley]

This thread is really going sideways
But I can share you 100% gold value has not changed the unit of measurement has changed

What are you talking about?

 

[Reefering1]

 

[Randy Holmes-Farley]

Just to clarify for others who may be reading this thread, no device that reefers use actually measures either specific gravity or salinity.

They measure other properties, such as density (hydrometer), refractive index (refractometer) or high frequency electrical conductivity (the Hannah and other conductivity meters).

Scientists have determined that these measured properties can be used to predict either the specific gravity or the salinity. All of them are impacted by temperature in ways that alter the relationship between the actual measured property and the predicted salinity or specific gravity. All of them except the glass hydrometer try to make this temp correction for you. In no case are these corrections due to any real change in salinity or specific gravity with temperature. They are correcting for how those other properties vary with temperature.

 

[TokenReefer]