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Keep in mind, these are two different methods of determining salinity. Both are inferential methods. One is optical while the other is an electrical measurement.
Impurities may affect one measurement method and not necessarily the other. In one case, a particular impurity may cause light to refract differently but it won’t have any influence on the conductivity. Example; let’s say you dumped some sugar in the sample. It will most definitely influence the refractometer, but the conductivity will hardly change at all. Conversely if you added some acid in the sample, the refractometer may not change much at all or might go lower while the conductivity goes higher.
Different salt mixes can also have an influence on the values. You might notice that one salt mixes to a certain specific gravity and spot on with thecexpected refractometer reading, but mix up a batch of a different brand of salt, and the conductivity might be higher or lower than the the expected refractometer’s equivalent reading. This shouldn’t be a huge difference, but it should be understood.
What’s important is that you get consistent readings with a fresh batch of salt and by doing regular water changes, you eliminate any impurities that cause optical or electrical interferences.
Impurities may affect one measurement method and not necessarily the other. In one case, a particular impurity may cause light to refract differently but it won’t have any influence on the conductivity. Example; let’s say you dumped some sugar in the sample. It will most definitely influence the refractometer, but the conductivity will hardly change at all. Conversely if you added some acid in the sample, the refractometer may not change much at all or might go lower while the conductivity goes higher.
Different salt mixes can also have an influence on the values. You might notice that one salt mixes to a certain specific gravity and spot on with thecexpected refractometer reading, but mix up a batch of a different brand of salt, and the conductivity might be higher or lower than the the expected refractometer’s equivalent reading. This shouldn’t be a huge difference, but it should be understood.
What’s important is that you get consistent readings with a fresh batch of salt and by doing regular water changes, you eliminate any impurities that cause optical or electrical interferences.
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