Salinity is your concentration of salt in your water, often reported through specific gravity (which is unitless) or salinity (in units of ppt, parts per thousand). Different tools test for Salinity using different units of measurement. Hydrometers use specific gravity, refractometers use refractive index, and conductivity probes use conductivity. The salinity of natural ocean water is 35ppt, corresponding to 1.0264 and 53mS/cm. At Coastal Reef we keep our saltwater between 1.024 and 1.026.