The Swell Super Defined Hydrometer is an economical, quick and simple way to determine the salinity within your salt water aquarium.
To use simply submerge the hydrometer in the tank, and when full turn it on its side. As the water pours out the guage will indicate the salinity level.
It is most accurate within 1.020 and 1.023 salinity and accurate to within 0.001. It is ideal for temperatures between 23 to 30⁰C, and performs as well if not better than other more expensive products from leading names.