Which Refractometer Calibration Fluid?

[Randy Holmes-Farley]

After you done calibrating with these 35 ppt soloutions Randy, did you ever had occsations where the refractro meter did not show 0 or almost 0 for RO or 0 TDS water? If so can you please tell what kind of values you normally get ?

Lots of people get substantially different results when calibrating with pure fresh water vs a 35 ppt standard. my article shows the difference you expect using a perfect brine refractometer calibrated with pure fresh water instead of a 35 ppt standard.
Both of the reasons I gave play a significant role in real world experiences.

 

[Randy Holmes-Farley]

Here is the pertinent summary section from it:

It turns out that this is a slope miscalibration in the sense that a perfectly made sodium chloride refractometer necessarily has a different relationship between refractive index and salinity than does seawater. This type of problem with a refractometer IS NOT at all corrected by calibrating it with pure freshwater. If you have this type of refractometer, and it was perfectly made and calibrated in freshwater, it will ALWAYS read seawater to be higher in salinity than it actually is (misreporting an actual 33.3 ppt to be 35 ppt).