Marine aquarium refractometer with automatic temperature compensation (ATC) for fast and easy measurement of sea water specific gravity and salinity. The meter has both specific gravity (1.000-1.070) and ppt (0-100ppt) scales.

Refractometer is an optical measurement device, which only needs a couple of drops of aquarium water for testing. Sea water is dropped onto the viewing plate, the plate cover is closed so that the plate is covered completely with water without air bubbles, the sample is allowed to adjust prism temperature for 30 seconds and the water sample is viewed through the refractometeer by pointing it towards a light source. Refractometer is purely optical unit and it does not need electricity to operate.

Refractometer is very accurate, but it needs to be calibrated in order to ensure best results. Calibration can be done with distilled water (specific gravity and ppt value 0.000) but it is recommendable to use water sample with the same specific gravity as natural sea water (35ppt). This can be done by mixing sodium chloride (NaCl; table salt) with distilled water. Recommended solution is 3,65g of sodium chloride and 96,35g (or ml) of distilled water, with which a refractometer is calibrated to 35ppt. (The total volume of the solution is 100g and 3,65g of salt gives a calculated value of 36,5ppt, but it must be noted that table salt is usually 97-99% pure sodium chloride and natural sea water also contains other salts than just NaCl).