Refractometer or Hydrometer?????
- Thread starter jimfed1
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MR PALM BEACH
New member
Refractometer all the way, 100% more pinpoint and accurate than a hydrometer. IMO hydrometer are really used for an estimate figure. A refractometer will tell you the exact salinity your salt level is at. This Is the one I use works pretty good.
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+4690+9957&pcatid=9957
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+4690+9957&pcatid=9957
MR PALM BEACH
New member
This Is what you see when looking through the refractometer.
http://www.peteducation.com/images/articles/ill_refractometer.jpg
http://www.peteducation.com/images/articles/ill_refractometer.jpg
tufacody
New member
If you have a hydrometer that is accurately labeled for 78 degree temp or so, then the hydrometer is golden. The problem is that they almost never come accurate. Mine was way off, and I didn't realize this until I purchased a refractometer. To be sure, I brought my refractometer to the LFS and compared it to a few of theirs. Once mine was calibrated with pinpoint salinity solution, it was spot on. I got a cheapie from Dr Fosters and Smith and it works as good as the LFS's $200 model. I have warned that the cheapies can be off, but haven't noticed that with mine.
Refractometers and conductivity meters (electrical salinity meters) are often more accurate than swing arm hydrometers. Floating glass hydrometers are also quite accurate.
All of these should be checked to calibrated with a seawater standard, or something close to it.
All of these should be checked to calibrated with a seawater standard, or something close to it.
How does the calibration work? I assume that is important.
Yes, it is. I discuss it here:
Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/index.php
from it:
http://reefkeeping.com/issues/2006-12/rhf/index.php#20
Tips on Calibrating a Refractometer
--------------------------------------------------------------------------------
Despite the fact that many refractometers sold to aquarists recommend calibration in pure water, such a calibration alone will not ensure accuracy for the reasons described above. So my recommendation for calibration is as follows:
1. First calibrate the refractometer in pure freshwater. This can be distilled water, RO (reverse osmosis) water, RO/DI water, bottled water and even tap water with reasonably low TDS (total dissolved solids). Calibrating with tap water that has a TDS value of 350 ppm introduces only about a 1% error in salinity, causing readings in seawater to read a bit low. So 35 ppt seawater (specific gravity = 1.0264) will read to be about 34.7 ppt, and will show a specific gravity of about 1.0261.
This calibration should ordinarily be carried out at room temperature using an ATC refractometer. The directions with some ATC refractometers insist that the calibration be carried out at a specific temperature, but I've never understood how that could matter and I would not worry about it. If the refractometer is not an ATC refractometer, then careful temperature control or correction is necessary, and such corrections are beyond the scope of this article.
Calibration is usually performed by putting the freshwater on the refractometer, letting it sit for at least 30 seconds so it comes to the same temperature as the refractometer, and adjusting the calibration screw until it reads a value appropriate for freshwater (e.g., refractive index = 1.3330, salinity = 0 ppt, specific gravity = 1.0000). Normally, this step is a quick and easy procedure, and may often be all that is required IF the refractometer has been verified to have passed the second calibration step below at least once. This is an offset calibration, as described above.
2. The second step in calibration should be performed at least once before relying on a refractometer to accurately measure the salinity of a reef aquarium. This step involves testing it in a solution matching the refractive index of 35 ppt seawater (or some similar solution near the range of measurement). Remember to let it sit for at least 30 seconds so it comes to the same temperature as the refractometer. Suitable commercial and do-it-yourself standards were described earlier in this article. Using one of them, place a drop onto the refractometer and read the value. If it reads approximately 35 ppt, or a specific gravity of 1.0264, or a refractive index of 1.33940, then the refractometer is properly calibrated and is set to go.
If it does not read correctly, and is off by an amount that is significant relative to your salinity precision requirements, then you need to recalibrate it using this second fluid. I suggest that a salinity error of ± 1 ppt or a specific gravity error of ± 0.0075 is allowable. If the refractometer is off significantly, and you used a do-it-yourself standard made with crude techniques such as Coke bottles, a good next step might be to buy a commercial standard.
To correct errors using these seawater standards, simply adjust the calibration screw on the refractometer until it reads the correct value for the standard (35 ppt, or a specific gravity of 1.0264, or a refractive index of 1.33940). This type of slope calibration makes the refractometer suitable to read solutions whose salinity is close to seawater's. After such a calibration, refractometers may not read freshwater correctly.
Again, despite the claims in the directions of some refractometers to have the standard at a particular temperature, when calibrating an ATC refractometer with this seawater standard, I'd just use it at room temperature.
If you are using a refractometer for hyposalinity, such as when treating a sick fish, I'd just use one calibrated in freshwater, because that is closer in salinity than seawater to the hyposaline solution usually used (say, specific gravity = 1.009). A new standard for hyposalinity can also be made by mixing one part 35 ppt seawater and two parts freshwater, but that is probably overkill.
Yes, it is. I discuss it here:
Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/index.php
from it:
http://reefkeeping.com/issues/2006-12/rhf/index.php#20
Tips on Calibrating a Refractometer
--------------------------------------------------------------------------------
Despite the fact that many refractometers sold to aquarists recommend calibration in pure water, such a calibration alone will not ensure accuracy for the reasons described above. So my recommendation for calibration is as follows:
1. First calibrate the refractometer in pure freshwater. This can be distilled water, RO (reverse osmosis) water, RO/DI water, bottled water and even tap water with reasonably low TDS (total dissolved solids). Calibrating with tap water that has a TDS value of 350 ppm introduces only about a 1% error in salinity, causing readings in seawater to read a bit low. So 35 ppt seawater (specific gravity = 1.0264) will read to be about 34.7 ppt, and will show a specific gravity of about 1.0261.
This calibration should ordinarily be carried out at room temperature using an ATC refractometer. The directions with some ATC refractometers insist that the calibration be carried out at a specific temperature, but I've never understood how that could matter and I would not worry about it. If the refractometer is not an ATC refractometer, then careful temperature control or correction is necessary, and such corrections are beyond the scope of this article.
Calibration is usually performed by putting the freshwater on the refractometer, letting it sit for at least 30 seconds so it comes to the same temperature as the refractometer, and adjusting the calibration screw until it reads a value appropriate for freshwater (e.g., refractive index = 1.3330, salinity = 0 ppt, specific gravity = 1.0000). Normally, this step is a quick and easy procedure, and may often be all that is required IF the refractometer has been verified to have passed the second calibration step below at least once. This is an offset calibration, as described above.
2. The second step in calibration should be performed at least once before relying on a refractometer to accurately measure the salinity of a reef aquarium. This step involves testing it in a solution matching the refractive index of 35 ppt seawater (or some similar solution near the range of measurement). Remember to let it sit for at least 30 seconds so it comes to the same temperature as the refractometer. Suitable commercial and do-it-yourself standards were described earlier in this article. Using one of them, place a drop onto the refractometer and read the value. If it reads approximately 35 ppt, or a specific gravity of 1.0264, or a refractive index of 1.33940, then the refractometer is properly calibrated and is set to go.
If it does not read correctly, and is off by an amount that is significant relative to your salinity precision requirements, then you need to recalibrate it using this second fluid. I suggest that a salinity error of ± 1 ppt or a specific gravity error of ± 0.0075 is allowable. If the refractometer is off significantly, and you used a do-it-yourself standard made with crude techniques such as Coke bottles, a good next step might be to buy a commercial standard.
To correct errors using these seawater standards, simply adjust the calibration screw on the refractometer until it reads the correct value for the standard (35 ppt, or a specific gravity of 1.0264, or a refractive index of 1.33940). This type of slope calibration makes the refractometer suitable to read solutions whose salinity is close to seawater's. After such a calibration, refractometers may not read freshwater correctly.
Again, despite the claims in the directions of some refractometers to have the standard at a particular temperature, when calibrating an ATC refractometer with this seawater standard, I'd just use it at room temperature.
If you are using a refractometer for hyposalinity, such as when treating a sick fish, I'd just use one calibrated in freshwater, because that is closer in salinity than seawater to the hyposaline solution usually used (say, specific gravity = 1.009). A new standard for hyposalinity can also be made by mixing one part 35 ppt seawater and two parts freshwater, but that is probably overkill.
MR PALM BEACH
New member
scroll down to how to calibrate, Its pretty easy.
http://www.grapestompers.com/articles/refractometer_use.asp
http://www.grapestompers.com/articles/refractometer_use.asp
Does the brand matter much? How about this one?
http://cgi.ebay.com/Salinity-Refrac...ryZ20755QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
http://cgi.ebay.com/Salinity-Refrac...ryZ20755QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
MR PALM BEACH
New member
Im not to sure on the brands but IMO they all seem to do the same thing. Hey If Its cheaper get It.
lloydkeller
New member
looks like the one i purchased off of ebay have had it a year super accurate have had no problems with it, but i payed 35.00
MR PALM BEACH
New member
You will be glad you got it, trust me.
You know, I have always wondered about my hydrometer, and the accuracy, as I could do it 3 times in a row and it would read different each time. I am reading more and more that exact salinity plays a major role in a reef. And now that I have a top off unit, I can keep things more precise and consistent.
You know, I have always wondered about my hydrometer, and the accuracy, as I could do it 3 times in a row and it would read different each time. I am reading more and more that exact salinity plays a major role in a reef. And now that I have a top off unit, I can keep things more precise and consistent.
scroll down to how to calibrate, Its pretty easy.
http://www.grapestompers.com/articl...tometer_use.asp
Just don't follow the advice in that link to use DI water for calibration., It won't be accurate for measuring seawater.
http://www.grapestompers.com/articl...tometer_use.asp
Just don't follow the advice in that link to use DI water for calibration., It won't be accurate for measuring seawater.
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