£89.99

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£33.99

A refractometer is a simple and robust way of accurately measuring the salinity within your aquarium and should be used by every serious marine aquarist.

The refractometer works on the principle of refraction of light to determine the salinity and is very accurate but also very simple and robust, unlike good quality glass hydrometers which are easily broken.

Light enters the instrument at one end and passes through a sample of the aquarium water which causes it to be refracted, (bends the light), depending on the salinity of the water. The refracted light is reflected off a scale inside and can be viewed through an eyepiece on the opposite end of the instrument.

What’s different between our NEW refractometer and others you might ask?

Almost all, if not all, of the refractometers currently available to the aquarium hobby are designed for measuring saltwater (sodium chloride or brine solution) and not true ‘seawater’. Although seawater is mostly sodium chloride it also contains other elements such as magnesium and calcium that change the refractive index slightly and will give a slightly different result.

The most common symptom of this difference in refractive index can be seen when mixing up salt as per salt manufacturer’s instructions and achieving a solution strength where it appears, through testing, that the levels of elements are lower than stated by the manufacturer. In actual fact all of the levels are low as the salinity is not as high as the aquarist believes – we have all seen low Ca or Mg for a given SG with almost all brands of salt.

It turns out that a 35ppt solution of true seawater has the same refractive index as a 36.5ppt solution of brine and so when using a brine/salt refractometer the salinity is likely to be low by 1.5ppt. This can be allowed for by the aquarist but only if they are aware of the difference.

After extensive development, D-D’s new refractometer addresses this issue, giving true salinity results when correctly calibrated and greater accuracy than previously attainable.
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