Most refractometers used within the aquarium hobby are not specifically designed for reef aquariums and use an algorithm for the measurement of brine (NaCl rather than seawater) and at a temperature of 15oC/59 0F rather than 25oC/77?0F. Thus, a measurement deviation of up to 1.5ppt is possible, which can have a significant adverse effect on coral growth and coloration.
Refractometer/ Hydrometer is a must if you're looking to setup marine aquarium. Please check the calibration first before using as mine wasn't calibrated properly. Please remember to calibrate with a sample solution or at least with RO water (experts say that RO water calibration may not be proper). Once it's calibrated properly, it's very easy to use to determine the salinity. Once again I have to Thank Indiefur for making all the aquarium products available under one roof.