salinity calibration confusion
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Randy Holmes-Farley
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I gave the exact reasons above in post # 17.
The response is approximately linear, but not all devices have the proper linearity even if made perfectly. A brine refractometer has a different slope of refractive index vs salinity than does a seawater refractometer (see the article posted just above for details in what that means). Even a true seawater refractometer may have the slope wrong if it is not made perfectly.
How many $50 analytical instruments are made perfectly?
Atrumblood
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Ok fair enough. Thanks again
GrizFyrFyter
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The quality of the equipment varies. I ran this test with the 4 refractometers we had at the LFS I worked at, just to show the manager why calibrating at 0 doesn't work.
One of the four was actually accurate with a 0 calibration. The other three were off by 0.002 to 0.007 sg.
You can use a commercial calibration solution but I have found several bottles that were not what they claimed to be and had a customer crash his tank after using a bad solution and making adjustments to his tank based off that calibration. His sg was 1.017 by them time he asked for help.
I prefer to either mix a calibration solution myself with a set amount of salt in a set amount of water (math doesn't lie) or use a floating hydrometer (not the swing style, the weighted glass meter that floats in the water) to check my refractometers monthly.
One of the four was actually accurate with a 0 calibration. The other three were off by 0.002 to 0.007 sg.
You can use a commercial calibration solution but I have found several bottles that were not what they claimed to be and had a customer crash his tank after using a bad solution and making adjustments to his tank based off that calibration. His sg was 1.017 by them time he asked for help.
I prefer to either mix a calibration solution myself with a set amount of salt in a set amount of water (math doesn't lie) or use a floating hydrometer (not the swing style, the weighted glass meter that floats in the water) to check my refractometers monthly.
Atrumblood
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The article was great. The graphs definitely helped me understand it better. Very nice write up @Randy Holmes-Farley
Randy Holmes-Farley
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Thanks.
Happy reefing.
Happy reefing.
