refractometer calibration

[DexterKarin]

Lately I feel a bit cursed. Have been using a digital salinity probe and come to find that it is 4 ppt off and my salinity was close to 40ppt! So I tried to calibrate it and it doesn't seem to hold a calibration. I had my friend a mechanical engineer try too, no luck.

Then I buy a refractometer. Using RO water to calibrate, I can't turn the screw to zero it out, won't turn any more. My RO water was tested at zero TDS but I haven't tested it recently. I'll go buy some distilled water to test refractometer but if that doesn't work, any other ideas or send it back? Is this common with these? Faulty I mean?

Thank you for any guidance.

 

[The_Paradox]

Calibrate with a known solution not distilled. At the end of the day none us know our exact salinity level but you should be able to get +\- 1 ppt not 4.

Here are two popular meters showing the difference between a known solution of 35ppt vs Distilled.

 

[DexterKarin]

Got it. Found it on Amazon. Thank you.

 

[gbroadbridge]

Got it. Found it on Amazon. Thank you.

For future reference it's easy to make a diy calibration solution using table salt.

https://reefkeeping.com/issues/2004-06/rhf/index.php