Bad refractometer calibration fluid

HeyJay · Sep 12, 2020

I've long been using a bottle of calibration fluid to double check my refractometer. Well after receiving a shipment of fish that were supposed to ship at 35ppt, I was quite confused when the water showed 30ppt. Even double checked with my spare refractometer.

At first I thought something was off in the shipping water but I just bought a different bottle of calibration fluid at the LFS and sure enough, my refractometer read 30ppt with that.

The original bottle doesn't expire for another year. Anyone else experience something like this?

Luckily my livestock has seemed mostly ok at what may actually have been around 1.028 salinity for an extended time.

Crabs McJones · Sep 12, 2020

I experienced exactly this a while back. I had a bottle.that I was calibrating to 1.026. When I got a brand new bottle I was actually at 1.030. I dont know if some of the water evaporated out raising the salinity or what.

John Rebman · Sep 12, 2020

Thats is why i use LAB Grade DI water ( Millipore 8AFS) to verify my refractometer. The 10Mohm water will read Zero ppt when calibration fluid used is 335ppt.
Any good quality DI water should read the same. It too easy to forget to shake the Calibration fluid once or twice and the salinity will increase. Also need to keep bottle shut tightly when not in use.
Good way to double check your refractometer.

John Rebman · Sep 12, 2020

John Rebman said:
Thats is why i use LAB Grade DI water ( Millipore 8AFS) to verify my refractometer. The 10Mohm water will read Zero ppt when calibration fluid used is 335ppt.
Any good quality DI water should read the same. It too easy to forget to shake the Calibration fluid once or twice and the salinity will increase. Also need to keep bottle shut tightly when not in use.
Good way to double check your refractometer.

that os suppose to be 35 ppt...oops!