If you have been using a hydrometer and have never tried a refractometer then you should really invest in one. They use much less water, and can easily be calibrated for accurate repeatable readings. For the most accurate readings you will want to calibrate the refractometer to the solution you will be reading, and that is why we always include a bottle of Aqua Craft Calibration Solution at 35ppt (1.026sg) to keep your reef tanks salinity spot on.
Must have equipment for aquarists! Easily and accurately measure the salinity of your tank. Simple to use and read. This unit automatically compensates for temperature. FREE Salinity Calibration Fluid included. Calibrating your unit ensures correct salinity readings. Refractometers are one of the best pieces of equipment an aquarist can purchase. It not only ensures accurate measurements of salinity but it is also infinitely easier to use and read.