Quote:
Originally Posted by sphelps
May I ask how much error you would expect and if you've actually tried it yourself?
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Actually, I haven't tried it myself because I have no use for a refractometer.
Without checking on the math of it, I believe the error is .0017 or thereabouts but I don't remember low or high just off hand. The answer is in that article.
There is NO WAY that an accurate refractometer that measures NaCl in water like the standard refractometer does, can read accurately throughout the scale measuring sea water with the many different salts involved as the refractive index is affected. If your NaCl refractometer calibrated with water is reading correctly at normal salt aquaria ranges, then it is a poor quality that has errors that just happen to read correctly at that range for some reason but it is scientifically not possible for a quality refractometer to do so.
I don't use a refractometer because I started over 18 years ago when everyone around here used either floating hydrometers or SeaTest swing arms.
As I already had a complete set of hydrometers from when I worked in a lab, that was my first choice, but I switched to using swing arms when I broke the floater that checked the range of the aquaria. I purchased a new Fisher Scientific certified calibrated floating hydrometer and a new columnar cylinder for measuring the s.g. in (I broke both hydrometer and cylinder at the same time). I also bought two SeaTest swing arms to use for everyday use so I wouldn't break another glass floater.
I used the certified hydrometer to check the swing arms, and one read slightly high and the other was slightly low.
With this older style you could remove the swing arm and so I shaved a touch off the weight in the arm of the high reader to make it read accurate at 1.026, and shaved a touch off the float material of the arm to allow the reading to rise to 1.026.
Now, I'm still using the swing arms, rinsing well after each use, soaking overnight in white vinegar once a week, and check once or twice a year against the certified, and it still reads accurately.