Hydrometer

A hydrometer is a device used to measure the specific gravity (sg) of water.

It is commonly used to measure the amount of salt in a body of water when setting up brackish or saltwater tanks. You'll want a hydrometer with a specific gravity scale of at least 1.005 to 1.030, salinity of 5 to 40.

Cheaper passive hydrometers are designed to be used at their calibrated temperature. Usually. If you measure at different temperatures you'll have minor errors.


 * For more accurate devices, see - Refractometer.

Links

 * Hydrometer Temperature Corrections
 * Hydrometer on Wikipedia