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Two of the most popular ways to measure salinity for aquariums are refractometers and conductivity meters. Our
HI96822 digital seawater refractometer is used to measure salinity via refractometry while our
HI98319 waterproof salinity and temperature meter measures salinity via conductivity.
What is refractometry?
With our HI96822 salinity determinations are made by measuring the refractive index of seawater. Refractive Index is an optical characteristic of a substance and the number of dissolved particles in it. Refractive Index is defined as the ratio of the speed of light in empty space to the speed of light in the substance. A result of this property is that light will “bend”, or change direction, when it travels through a substance of different refractive index.
What is conductivity?
Conductivity is most commonly defined as a substance’s ability to transmit heat, sound, or electricity. Small charged particles called ions help to carry the electrical charge through a substance. These ions can be positively or negatively charged. The more ions available the higher the conductivity; fewer ions will result in lower conductivity. Also, the higher the conductivity, the higher a solution’s ability to conduct electricity. This is a result of a large number of charged ions present in the solution. Since the various elements used to make up salinity carry an ionic charge, conductivity is used to determine their gross concentration in water.
What is better for salinity?
When comparing conductivity to refractometery to measure salinity, the consensus among the scientific community favors conductivity. This is because there are non-conductive material 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 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, 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.
Important Information about our HI98319
1. You cannot use the calibration solution for refractometers. The calibration solution is a 35ppt conductivity standard based off of the International Oceanographic Tables
2. The calibration solution is a one time use and cannot be reused after calibration
