Refractometer or hydrometer
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Finnaddict
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I would trust the Refractometer reading. Much more accurate than a Hydrometer.
Finnaddict
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hydrometers may be consistent but not accurate. Temp has nothing to do with it. These are tools to measure salinity and the refractometer is the best one.
Randy Holmes-Farley
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FWIW, maybe they will read closer at 1.009,which is what matters, not whether they can read 1.024 correctly.
In any case, you can check either one with an appropriate test solution. If you have a balance I can detail how to make one with table salt for each device.
In any case, you can check either one with an appropriate test solution. If you have a balance I can detail how to make one with table salt for each device.
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Actually, temp can have a lot to do with it. Most refractometers are auto temp calibrating. Most hydrometers are calibrated to a certain temp, so if your water isn't at that temp, your hydrometers will be off.
Randy Holmes-Farley
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fwiw means for what its worth
I have recipes for making calibration solutions (different ones) for hydrometers, refractometers, and conductivity probes.
If you have a good balance, they will be very accurate. If you just want a rough check, I have recipes that make use of measuring cups and such.
Here's my refractometer recipe:
Make a 3.65 weight percent sodium chloride solution by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water. That amount roughly corresponds to ¼ cup (73.1 g) of Morton's Iodized Salt dissolved into 2 liters (2000 g) of water (giving very slightly more than 2 L of total volume).
For a rougher measurement in the absence of an accurate water volume or weight measurement:
1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Add 1 teaspoon of salt (making about 79.3 g total salt)
3. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified fresh water (about 2104.4 g)
4. Dissolve the total salt (79.3 g) in the total water volume (2104 g) to make an approximately 3.65 weight percent solution of NaCl. The volume of this solution will be slightly larger than the Coke bottle, so dissolve it in another container.
How to Use a Refractive Index Standard
One simple way to use this refractive index standard is to measure it with a refractometer, and just remember what setting the standard came to. That setting represents S=35 seawater. Hopefully, the reading of the refractometer at that point will be similar to the properties of 35 ppt seawater (specific gravity = 1.026 - 1.027, or S=35, depending on the units). Simply using it as the target salinity for the aquarium is a fine way to go.
Alternatively, one can actually calibrate the refractometer using the standard by adjusting it until it reads the appropriate setting. Exactly how to adjust it depends on the refractometer, but often it is as simple as turning a screw.
I have recipes for making calibration solutions (different ones) for hydrometers, refractometers, and conductivity probes.
If you have a good balance, they will be very accurate. If you just want a rough check, I have recipes that make use of measuring cups and such.
Here's my refractometer recipe:
Make a 3.65 weight percent sodium chloride solution by dissolving 3.65 grams of sodium chloride in 96.35 grams (mL) of purified fresh water. That amount roughly corresponds to ¼ cup (73.1 g) of Morton's Iodized Salt dissolved into 2 liters (2000 g) of water (giving very slightly more than 2 L of total volume).
For a rougher measurement in the absence of an accurate water volume or weight measurement:
1. Measure ¼ cup of Morton's Iodized Salt (about 73.1 g)
2. Add 1 teaspoon of salt (making about 79.3 g total salt)
3. Measure the full volume of a plastic 2-L Coke or Diet Coke bottle filled with purified fresh water (about 2104.4 g)
4. Dissolve the total salt (79.3 g) in the total water volume (2104 g) to make an approximately 3.65 weight percent solution of NaCl. The volume of this solution will be slightly larger than the Coke bottle, so dissolve it in another container.
How to Use a Refractive Index Standard
One simple way to use this refractive index standard is to measure it with a refractometer, and just remember what setting the standard came to. That setting represents S=35 seawater. Hopefully, the reading of the refractometer at that point will be similar to the properties of 35 ppt seawater (specific gravity = 1.026 - 1.027, or S=35, depending on the units). Simply using it as the target salinity for the aquarium is a fine way to go.
Alternatively, one can actually calibrate the refractometer using the standard by adjusting it until it reads the appropriate setting. Exactly how to adjust it depends on the refractometer, but often it is as simple as turning a screw.
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