Refractometer

Definition

A refractometer measures the refractive index of saltwater to determine salinity. The reef-keeping standard tool for checking SG.

Practical use

Calibrate monthly with a 35 ppt calibration solution. Place 2-3 drops of tank water on the prism, close the cover plate, hold up to light, read the SG line on the scale. Cheaper than the alternative (digital salinity meters cost more, hydrometers drift).

Browse the full glossary for more aquarium terms.