The Red Sea Seawater Refractometer offers exceptional accuracy, designed to determine absolute salinity at a temperature of 25 ^o C.

To exclude measurement errors, the refractometer was calibrated to 25°C, as room and water temperature influence the measurement result. The special seawater calibration of the prism ensures additional measurement accuracy. Compared to standard refractometers (NaCl calibration), deviations of up to 1.5 per mille (‰, ppt) can occur when measuring seawater, which can affect coral growth and coloration.

The Red Sea Seawater Refractometer Video

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The main features of the new refractometer are:

• Instant reading of the absolute salinity of seawater at 25°C (no compensation factors for seawater or temperature required)
• Specially tailored to the ion content of seawater and developed for precise measurement of salinity. (Most standard refractometers are only calibrated with a standard salt solution (NaCl))
• Seawater calibration at 25°C (normal temperature for saltwater aquariums. Most standard refractometers are calibrated at 15°C)
• Easy to use thanks to the easy-to-read, high-resolution display with the measuring range up to 40 per mille (‰, ppt), which is important for seawater.
• Easy calibration with reverse osmosis water.
• Includes automatic temperature compensation (ATC) for accurate measurement results regardless of room temperature

The Red Sea Seawater Refractometer Display

The per mille scale (PPT) of the Red Sea seawater refractometer is calculated using an algorithm based on seawater and thus the reading gives the absolute salinity of seawater.

The parts per thousand (PPT) scale of conventional salinity refractometers is calculated based on an algorithm of table salt. Using a table salt refractometer on sea water can result in deviations in the reading of around 1.5ppt of the salinity value.

The Red Sea Seawater Refractometer Display	Typical salinity display

About Salinity

Salinity is a general term that describes the concentration of salt in a water solution. The different types of salts also have different refractive indices.
A saline solution of sodium chloride consists of 2 chemical elements.

Seawater, on the other hand, consists of about 70 chemical elements, such as calcium, magnesium, potassium, etc., in addition to sodium chloride.

Therefore, seawater and saline solution with the same salinity (ie the same weight of salt/liter) have different refractive indices and give different salinity values ​​when measured on the same refractometer

refraction & refractive index

All transparent materials such as liquids refract (distort) light.

All transparent materials refract light differently and have what is called a “refractive index,” which shows the degree of distortion of a particular material in light.

Different concentrations of the same liquid have different refractive indices.

The scale of a refractometer is calculated by a mathematical algorithm that relates the measured refraction to the concentration of a particular liquid.

refractive index and temperature

The refractive index of liquids changes at different temperatures, which has a significant influence on the measurement result of salinity with a refractometer.

The algorithm for determining the PPT (and SG) scale for a refractometer is calculated based on a specific temperature.

PPT readings from refractometers that have not been calibrated for reef aquariums (eg 25°C) must be adjusted to the appropriate aquarium temperature using a conversion table to display the appropriate PPT value. This is often the cause of misinterpretation of refractometer readings.

For example: When using a seawater refractometer calibrated to 20°C, the PPT reading will be approximately 1-1.5 ppt lower than the absolute salinity of the same water sample at normal aquarium temperature of 25°C.

Because the Red Sea Seawater Refractometer is calibrated to 25 ^° C, an immediate reading of the absolute salinity is possible (no compensation factors necessary).

ATC – Automatic Temperature Compensation

Temperature is probably the most common cause of inaccurate readings from a refractometer. Calibration and testing of water samples is essential before the refractometer and water sample are adjusted to the correct temperature.

Automatic Temperature Compensation (ATC) compensates for a few degrees difference between the ambient temperature and the refractometer's calibrated temperature. Larger temperature fluctuations will result in an approximate deviation of about 1.0ppt in the salinity reading.

ATC cannot adjust the PPT scale of the refractometer to the temperature of the aquarium!