HI98319 is a digital salinity tester designed specifically for saltwater aquariums that displays results in parts per thousand (ppt), Practical Salinity Units (PSU), or specific gravity (S.G.). This waterproof tester uses an amperometric conductivity probe to determine the salt content in the water. Exposed Temperature Probe for Fast Response Measures salinity up to 70.00 ppt Waterproof and designed to float