A new Red Sea Seawater Refractometer is setting the bar a bit higher for other refractometers. Many of us started out in the hobby with a hydrometer of some sort and when we graduated to the refractometer, it was like night and day. Now, thanks to the new Seawater Refractometer, there is another reason to get excited about this handy instrument.
The first thing that caught our eye was the crisp blue and white division on the scale and the larger numbers making it easier to read but as we started peeling back the layers, we learned there was way more value with the Red Sea Seawater Refractometer.
First off we learned traditional salinity refractometers were built to read salinity levels in brine — normal sodium chloride with just two elements. Conversely, seawater has over 70 chemical elements that go way beyond sodium chloride including calcium, magnesium, potassium and more. Why does this matter?
Take seawater and brine of the same salinity and you will find there are two different refractive indexes that can lead to an error of around 1.5 PPT in your reading. The secret sauce to this device is the salinity scale of this refractometer being calculated using their own algorithm for seawater, giving you a reading of the absolute salinity of seawater.
On top of this, the refractometer is also calibrated to a higher temperature of the liquid being tested (25 degrees Celsius or around 77 degrees Fahrenheit) to give you a more accurate reading that can lead to another discrepancy of 1-1.5 PPT. I know what you’re thinking, my refractomer has ATC or automatic temperature compensation. But according to the Red Sea literature, this only takes into account differences in ambient air temperatures not the water sample being tested
We go through all the efforts to accurately read all the different levels in our tanks and our handy refractometer can be giving us erroneous readings up to 3 PPT — quite a drastic difference. These are available now in the UK and go for around £45 (about $77 USD).