Calibrating a refractometer is pretty simple, but there are some key points that you should make sure you are doing to get the most accurate readings. Almost all prism style refractometers can be calibrated to a full range of solutions, and it is best to use a solution that is relatively close to the final reading you desire. For a reef tank and most other saltwater aquariums, we highly suggest calibrating refractometers to 1.026 sg or 35 ppt, using Pinpoint’s Calibration Solution. Usually calibration is only required once every couple months, however, the more often you do it will ensure accuracy and reliability.
By placing a couple of drops of calibration solution on the sight glass and closing the diffusion cover over the liquid will allow you to look through the eyepiece of the refractometer to see if any adjustments are required. By removing the small black cap that protects the adjustment dial, you can manipulate the final reading to match your calibration solution.
Once your refractometer is calibrated, you can then rinse off any residual calibration solution and use it for your aquarium!