Glass hydrometer (bobber) and Salinity at Room Temp

[ihavecrabs]

Randy,

As Salinity doesn't change with temperature, what effects do I need to be aware of for the glass bobber style hydrometer?

I'm mixing my salt water for an ATS system which will be at room temperature or cooler since it will be newly filtered RODI.

Does the hydrometer self manage temp using buoyancy or so I need to correct manually?

Thanks!

 

[ahammer]

Hi ihavecrabs,

I have not used one of those style hydrometers in a few years, but as I remember there is a manual correction that needs to take place. There should be a temperature on the hydrometer or packaging it came with that is standardized and you must correct for any degrees above or below said temperature.

 

[ihavecrabs]

Hi ihavecrabs,

I have not used one of those style hydrometers in a few years, but as I remember there is a manual correction that needs to take place. There should be a temperature on the hydrometer or packaging it came with that is standardized and you must correct for any degrees above or below said temperature.

Thank you. It looks as if it is calibrated to 77F. Thanks!

Is there a set number to adjust by per degree or is it not a linear relationship?

 

[ahammer]

I do not remember at this time, I apologize. It has been too long! I know that you can find Hydrometer Temperature Adjustment Calculators on your search engine to help out with this. Many beer brewers use this as well.

 

[jimk60]

I have used the same hydrometer for almost 30 years. It's calibrated for 75 degree and must be converted for temp. Even though I use a refractometer I still check it with the hydrometer because it is always spot on.

 

[Randy Holmes-Farley Verified Community Expert]

Randy,

As Salinity doesn't change with temperature, what effects do I need to be aware of for the glass bobber style hydrometer?

I'm mixing my salt water for an ATS system which will be at room temperature or cooler since it will be newly filtered RODI.

Does the hydrometer self manage temp using buoyancy or so I need to correct manually?

Thanks!

The reason you need a correction is that the density of the water changes as a function of temp due to expansion as the temp rises, glass changes much less (almost none in this context). Since the height the hydrometer floats depends on the density of the water, the reading changes with temp.

There are many online tables for correcting hydrometers with typical calibration temps.