Versatile swing-arm hydrometer accurately measures both specific gravity and water temperature. Clever design allows periodic or continuous reading of the most important water quality parameter in saltwater aquariums. Measure from 1.010 to 1.030 specific gravity and 64-97°F.
Please click on "More Information" for directions, specific gravity conversion charts, and salinity information.
|Directions for Use
Continuous Real-time Measurement
Hydrometers, Salinity, Specific Gravity, & Temperature
The most basic water quality parameter in a saltwater aquarium is the Salinity, which is a theoretical measure of the amount of salt contained within a volume of water, normally expressed as grams per liter (g/l) or parts per thousand (ppt). (Note: Salinity should not be confused with manufacturer's instructions for the preparation of artificial seawater expressed in g/l or lb/gal.)
Unfortunately, it is not possible to measure Salinity directly. However, it has a temperature-dependent relationship with Specific Gravity, which is easily measured with a hydrometer. For a particular Salinity, specific gravity increases with decreasing water temperature and ,therefore, a S.G. measurement is only meaningful if the temperature is also known.
Conversion of S.G. to Salinity at a constant temperature of 25°C/77°F
Effect of temperature on S.G. for a constant Salinity of 30.6 ppt
Salinity in the Saltwater Aquarium
It is essential to maintain correct salinity in a saltwater aquarium because of the fine balance between the concentrations of salts in a fish's body tissue, compared with that of the surrounding water. The ability fish have to control small fluctuations of these concentrations in nature is called osmoregulation. However, if the salinity of the water in an aquarium is outside the range of naturally occurring salinities, then fish and invertebrates will experience osmotic stress, which can lead to their death.
The most common occurrence of salinity variation is the gradual increase in Salinity due to evaporation. Constant and accurate measurements of S.G. are, therefore, essential to ensure correct conditions. A salinity of 30.6 ppt, i.e. a specific gravity of 1.021 at 25°C/77°F is recommended for most saltwater aquariums.