Thank you everyone for your feedback and we appreciate your support/comments. Wanted to share a few points on comparing refractometers to electrical conductivity meters like our HI98319 salinity meter. This information can be found on our blog posted here:
http://blog.hannainst.com/salinity-measurements-in-aquariums
There are a number of ways to perform salinity measurements in your aquarium. The most well-known methods by marine aquarists include using hydrometers, refractometers and conductivity meters. A method commonly used for aquariums are hydrometers, particularly swing-arm models. These can be problematic as they do not compensate for sample temperature, need to be hydrated with sample prior to use and can be prone to inaccuracies. Optical refractometers designed for seawater also have downsides. Even though calibration solution exists, determining salinity can be difficult and not always easy to read. Optical refractometers are often calibrated to a specific temperature range and if your sample temperature does not fit in that range, your results can be skewed.
Conductivity is a measurement of the dissolved ionic solids present in the water. Additionally conductivity may also be used as a means to measure salinity, as the salts become ions when dissolved in water that can conduct an electrical current sensed by the meter and measured in mS/cm. Temperature is important when reading salinity as the mobility of ions increases when the water becomes warmer or slower when cooler.
When comparing conductivity meters to refractometers to measure salinity, the consensus among the scientific community favors conductivity. This is because there is often non-conductive material in your sample which can impact the refractive index of seawater but not the actual salt concentration. For example, if we add sugar to artificial seawater, we will see that our salinity value will increase on a refractometer but we have not changed the concentration of salt in the water. If we measured the salinity of that sample with our HI98319 conductivity meter you’ll notice the value is largely unchanged. It is common to have inflated values with a refractometer due to the large number of materials which will affect the density of that water outside of the dissolved salt values. For example, anti-caking agent in salt mixes, organic waste, sugars, potential non-ionic contaminants or uneaten fish food can increase the values produced on a refractometer but this would be less likely to occur on a conductivity meter like the
HI98319. Added bonuses of using conductivity to measure salinity are that you no longer have a light interference, and the temperature compensation is of your direct sample and not as influenced by ambient atmosphere near the surface of a prism.
