Continuous or periodic reading of specific gravity for saltwater aquariums Accurate measurement of specific gravity Easy to read digital thermometer User friendly patented design The most basic water quality parameter in a saltwater aquarium is the Salinity. The unique, patented design of Red Sea’s hydrometer enables the hydrometer to be installed permanently inside the aquarium or sump giving a continuous “real-time” reading of S.G. in addition to being used as a regular hydrometer for periodic S.G. measurements. The Hydrometer includes a digital thermometer to ensure that the water being tested is at the correct temperature.