When you need absolutely accurate salinity conditions in your aquarium, you're going to need an H2 Ocean Seawater Refractometer. Unlike other refractometers on the market, the H2 Show Refractometer measures "true" seawater salinity levels, instead of just saltwater. This means that it measures usually unaccounted for elements such as calcium and magnesium as well as sodium chloride, giving highly accurate, precise results.
True calibration of your seawater levels creates the ideal environment for fish to thrive. Other features include a finer scale running from 20-40ppt salinity (SG 1.015 - 1.030), 20/20 calibration at room temperature for more consistency and accuracy in everyday use, and full ATC (auto temperature compensation) ranging from 5 to 30 degrees C.