Hand-held instrument for the measurement of the TRUE Salinity and Specific Gravity (S.G.) of seawater by refractive index.

What is different about the D-D Seawater Refractometer?

Almost all handheld saltwater refractometers available to the hobby are designed and calibrated for testing brine solutions (e.g., sodium chloride) and are not calibrated for the refractive index of natural seawater.

Even though the largest percentage of salt in the sea is sodium chloride, the presence of other significant ions, such as magnesium and calcium, in natural seawater results in a different refractive index relative to that of brine. A standard salt (brine) refractometer will therefore not give the correct salinity for natural sea water (NSW), and a conversion factor must be applied.

For example, a 35ppt solution of NSW has the same refractive index as a 36.5ppt solution of brine.

After extensive development, D-D’s new ATC refractometer addresses this issue by calibrating the scale for seawater, providing true salinity results for aquarium use when properly calibrated and greater accuracy than previously attainable.

Our refractometers feature a copper internal body, which conducts heat faster than cheaper aluminum and plastic versions, enabling faster, more accurate auto temperature compensation.

Further reading here: https://www.theaquariumsolution.com/product/3034/123