Quick Refractometer Question

[zachj7]

I have an ATC Refractometer, and for the past decade have been guilty of calibrating it with clean RO/DI at 0. Never spent much time on reef forums until now. It's obvious now that isn't the best way, I now have a calibration fluid for 1.026, and calibrated it on that. I would have assumed even after calibrating at 1.026 and then checking the RO/DI water that it would have been at least somewhat close to 0, but it is quite a bit off at around .005 below 1.000. Is this typical? Or is something wrong here.

Apparently I have been reefing for 10 years at 1.022 now that i have it calibrated with a calibration fluid instead of using 0...

 

[Eric1493]

I think that that has to do with the inaccuracy of the refractometer in terms of the slope between the measured refractive index and actual refractive index. For that reason, you are supposed to calibrate the refractometer with a solution closest to the measurement that you are taking. You can read more abt it here: http://reefkeeping.com/issues/2006-12/rhf/index.php

 

[Eric1493]

To answer your question, if the calibration solution is correct, your refractometer is calibrated, but it will only be accurate at 35ppt. Because of this, measurements taken very far from 35 ppt will likely be inaccurate. I would trust the calibration solution.

 

[zachj7]

Thanks, just really needed a sanity check. Thought I was going crazy when the calibration fluid showed up as 1.030 on the improperly calibrated refractometer.