When it comes to measuring Salinity, refractometers are one of the most accurate tools available to reefkeepers. Thankfully, they are also relatively inexpensive and straightforward to use. What many hobbyists may not be aware of though is that not all refractometers are created equal, indeed, some are actually calibrated to measure a saltwater ‘brine’ solution rather than true seawater. Although still useable, this can mean that the reading obtained from such units can be slightly misleading to the unsuspecting hobbyist. To-date, refractometers calibrated for true seawater have been few and far between but a new option has recently become available from Red Sea.
For this hands-on review, we received one of Red Seas brand new REEF-SPEC seawater refractometers a few weeks ago and we immediately integrated it into our equipment set to see how it would hold-up under typical day-to-day use. Firstly, let’s say the presentation of this refractometer is excellent. Packaged in a sturdy ABS box with a rugged clip system plus internal padding to hold the components securely, this is one neat package (and all that we’ve come to expect from a specialist operation like Red Sea). All the tools needed to both calibrate and use the tool are included and of good quality, along with some brief but comprehensive instructions. All good so far!
In practice, this refractometer is simple to use and very similar to other units we’ve handled over the years. That said, this isn’t just a rebadge of a generic unit by the looks of it, as this unit does have a twisting eye piece that allows the scale to be focussed very sharply. We’d hazard a guess that, in addition to the unit itself, the optics are of slightly better quality and this should prove really useful for those of us with less than perfect vision. On top of this, the display differed from our brine unit in that the scale was generally crisper and the numbers were larger. The other major difference between this unit and the plethora of brine units available is the scale itself and immediately one can see this is refined to a range that is of particular relevance to reef aquarists. Red Sea state ‘The PPT scale on Red Sea’s Seawater refractometer is calculated using an algorithm for seawater and therefore claims to give a reading of the Absolute Salinity of seawater’. Calibrated to read zero with glass-distilled water on the plate, and by turning a small screw with the included flathead screwdriver, this ‘zeroed’ unit gave our test system a reading of 35ppt whereas the brine unit we’d been using gave us a reading of approx. 37ppt. This fits in with the idea that brine units generally read around 1.5ppt lower than they should. After we had taken the reading we dried-off the unit carefully and put it into storage for a week. When we came to use it again we found that the unit didn’t need to be recalibrated as a few drops of distilled water still read zero on the scale. In short, the unit performed exactly as it should have, with no issues whatsoever.
At £39.99 RRP (average online price, at time of review), this refractometer is slightly more than your typical brine refractometer but of course it does offer an enhanced level of accuracy. On top of this, the build quality, optics and packaging are top notch and this seems to combine to give a high level of reliability also. Given that a low Salinity level can have knock on effects on other aspects of water chemistry, mineral levels for example, we’d highly recommend this precision instrument not just for all hobbyists, but particularly for those maintaining high demand stony coral systems.