Calibrating refractometer

[EvilE]

I recently got a refractometer, and I calibrated it, and used it. My question is how often should I calibrate it?? Once a week, before each use, what??

 

[crumbletop]

Once you get it calibrated, you just need to check it from time to time. Mine holds its calibration really well. Don't calibrate with RO, though -- even though that is what the manual says. The only reliable method for calibration, IMO, is to make up some calibration standard based on this article:

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

Here is a good article on refractos:

http://reefkeeping.com/issues/2006-12/rhf/index.php

The second article mentions pinpoint salinity calibration solution as being okay for refractos, but I have found them to be unreliable (checked 8 bottles of the stuff). Others have found the same, such as this post here:

http://reefcentral.com/forums/showthread.php?s=&threadid=1007891

Another way to calibrate would be to find someone with a good floating glass aquarium hydrometer, and calibrate your refracto to the SG measured by the hydrometer. Your LFS may have one.