Throw away the hydrometer and pick up a Deep-water Aquatics Refract meter for truly accurate salinity measurements. The Deep-water Refract meter should be calibrated before use.
A New finer scale running from 20-40ppt salinity (SG 1.000 - 1.070)
20/20 calibration at room temperature for more consistency and accuracy in everyday use
Full ATC (auto temperature compensation) ranging from 5 to 30 degree C