Use the Aqua One Glass Hydrometer to measure the density of salt within your aquarium.
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Red Sea’s Seawater Refractometer offers exceptional accuracy, for measuring the absolute salinity of seawater at a temperature of 25oC/77 0F.
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.
Red Sea’s Refractometer display:
The PPT scale on Red Sea’s Seawater refractometer is calculated using an algorithm for seawater and therefore will give a reading of the Absolute Salinity of seawater.
The PPT scale on regular salinity refractometers are calculated using an algorithm for Brine. Using a Brine refractometer for Seawater will give an error of approximately 1.5ppt in the salinity reading.
Salinity is a general term describing the concentration of salt in water. However, solutions of different type of salts have different refractive indexes.
Brine is a solution of Sodium Chloride (table salt) that contains 2 chemical elements.
Seawater contains approximately 70 chemical elements that include Calcium, Magnesium, Potassium etc. in addition to the Sodium Chloride.
Seawater and Brine of the same salinity (i.e. the same weight of salt/liter) have different refractive indexes and will give different salinity readings if measured on the same refractometer.