Salinity is one of the most critical parameters to control in a reef tank, yet also one of the most frequently misunderstood. This confusion arises perhaps out of a passing similarity of the term Salinity to ‘Specific Gravity’ (SG for short) which is a measurement also often used to gauge the ‘saltiness’ of water. SG is only part of the equation needed to establish Salinity though, indeed temperature must also be taken into consideration with the SG reading to give you your final Salinity reading (take a look at the chart here). Although natural seawater can range in Salinity from 30 – 40ppt in certain seas (or even certain microhabitats), 35ppt is the average and the level that most hobbyists target.
Using a refractometer allows one to attain a Salinity reading without recourse to the chart outlined above, and is generally one of the most convenient and cost-effective ways to assess your system Salinity accurately on a day-to-day basis. The Vertex RF1 is a ‘saltwater’ refractometer, therefore it is designed to measure Sodium chloride content, rather than actual Seawater (which contains additional minerals etc). Most refractometers offered to hobbyists are of this kind actually, and this isn’t a problem assuming a couple of points are taken into account. Firstly, due to differences in the mineral content of saltwater and seawater, it is wise to calibrate such a refractometer with 53ms/35ppt calibration fluid or, if using distilled water to calibrate a zero point, aim for a slightly higher seawater reading to compensate (37ppt). The differences are minimal, actually, but it’s always worth aiming for the highest level of accuracy reasonably possible. Although this is a temperature compensated refractometer, always take the time to allow the sample a minute or so for the temperature equalise. Having both the unit and the sample at 20c gives the most accurate result (to read more about this subject click HERE).
So, regarding the unit itself, we think this is a solid piece of equipment capable of acceptable accuracy if standard guidelines are followed. In terms of build quality, this is easily the best refractometer we’ve used to date. The stainless steel and rubber construction feels excellent quality and we are sure this will give you years of service if you look after it properly. Critical to this, the hard case it comes in is also top quality and all the relevant accessories are included, including a soft cleaning cloth. If you are in the market for one of these useful devices definitely consider the RF1, and take note that it is now available in the UK through Marine Aquatics for £32.99