Salinity question

[Thespammailaccount]

@Randy Holmes-Farley
Trying to figure out what the specific gravity would be but the online calculators don’t have an option to change the temp

 

[fishguy242]

#reefsqaud ??

 

[Randy Holmes-Farley Verified Community Expert]

#reefsqaud ??

not needed lol

 

[Randy Holmes-Farley Verified Community Expert]

@Randy Holmes-Farley
Trying to figure out what the specific gravity would be but the online calculators don’t have an option to change the temp

There are many different ways to answer this question. The best answer will depend on what you actually want to know, since I think the literal question is not what you are truly interested in.

Specific gravity itself, at a fixed salinity, hardly changes at all with temperature, unless the temp changes are large. Hydrometer readings may change, as may refractometers, and even conductivity meters, if they are not temp corrected.

 

[Randy Holmes-Farley Verified Community Expert]

If you really want the sg at 18 deg C for 28 ppt seawater, here's one way to get an answer.

The density of 28 ppt seawater at 18 deg C is about 1.020 g/cm3

Salt Water Density Calculator • Hydraulics — Fluids • Online Unit Converters

This salt water density calculator determines the density of salt water with salinities between 0 and 43 ppt, temperatures between 2 and 40°С and pressures ...

www.translatorscafe.com

or

Utilities: seawater density

The density of pure fresh water at 18 deg C is about 0.9986 g/cm3

Water Density, Specific Weight and Thermal Expansion Coefficients - Temperature and Pressure Dependence

Data on the density and specific weight of water across various temperatures and pressures. Useful for engineering, fluid dynamics, and HVAC calculations.

www.engineeringtoolbox.com

So the sg of 28 ppt seawater at 18 deg C compared to freshwater at the same temperature is

sg = 1.020/0.9986 = 1.0214

 

[Thespammailaccount]

I came across a paper that I am interested in trying to replicate for a culture of zooplankton for a type of fry but I can’t figure out what the specific gravity or even PPT would be at a temp of 32 degrees Celsius

 

[Randy Holmes-Farley Verified Community Expert]

oops, not sure why I thought that was 18 deg C.

i also would not be sure the person writing it knows what they are doing, and that the value isn't just a hydrometer or refractometer reading at that temp (which is technically wrong but may be what they meant).

But here's the redo at 32 deg C.

28 ppt seawater at 32 deg C density = 1.01585

Freshwater density at 32 deg C = 0.99505

sg = 1.01585/0.99505 = 1.0209

Note that is why I said it actually doesn't vary much The change in true sg from 18 to 32 deg C in sg is quite small (1.0214 to 1.0209).

 

[Thespammailaccount]

Thank you so much been 20 years I forgot I was working with density. I wondered how pressure would affect salinity and at 1 decibar it was approximately 1.0209 and at 1000 decibar it was approximately 1.0251 if I did the math correct

 

[TriggerFinger]

 

[Thespammailaccount]

I was scratching my head too until @fishguy242 said just make a post thank you

 

[Thespammailaccount]

Thank you @Randy Holmes-Farley

 

[Randy Holmes-Farley Verified Community Expert]

Thank you so much been 20 years I forgot I was working with density. I wondered how pressure would affect salinity and at 1 decibar it was approximately 1.0209 and at 1000 decibar it was approximately 1.0251 if I did the math correct

Very, very little unless you are in the deep ocean.