The specific gravity readings in the table to the left range from 1. The difference between the readings is due solely to the calibration temperature which is used to set the scale for the instrument. From this we can see how non specific S. D-D refractometers are calibrated at 20 C and so the calculated specific gravity at 35ppt displays a reading of 1. This is the equivalent to a specific gravity reading of 1. For further detailed information regarding salinity and specific gravity measurement please read the article on our website at:.
Skip to main content. Toggle navigation. About Products Support Gallery Contact. Steriliser Units UltraFlow Weir comb. K Deltec Spares U. Get Help. Specifically designed for aquarium use for measuring the salinity of Natural Sea Water.
Can you tell me which pen type you bought? I happened to come across the pen types on Amazon while looking at the manual ones. Some had no reviews but one of them had a couple reviews and they were all positive 4 to 5 stars.
Having said that I would like to know which one you bought as that would probably be the safest. I agree with Ian that all products have good manufacturers and bad manufacturers so life would be easier to get one that someone already swears by as being great. I hope he follows up with which brand he uses hopefully he is located here in the USA, so we can both easily get one!
I have a friend with one of the manual types so I can borrow that to compare the readings. How exciting, saltwater tanks really are something else. They are a lot of work though, but the fish you can keep are absolutely stunning.
That would be really awesome if you could road-test the pen type refractometer! I hope your set up goes smoothly. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Sign up with your email for our newsletter and be notified when we publish new blog posts. Close Menu Blog. Aquarium thermometer. Automatic fish feeder.
Water changer. Tags Salt Water Chemistry. Comments Thanks again for your post! Hi Karen, I have no experience with the pen-style refractometers. Keep writing those articles. Hi Rob, Like all test equipment, you can get good equipment and bad ones.
Open the cover and wipe the prism with a soft cloth to remove fingerprints. There should be no salt residue on the prism or cover. Rinse with RO water if necessary and dry with a soft cloth. Add a few drops of calibration solution to the prism and close the cover.
Wait about 45 seconds for the ATC to correct for temperature. If the reading does not match the calibration solution, make small adjustments with the calibration screw. Tips for Accurate Readings Keep the prism free of fingerprints. Use a soft eyeglass cloth to keep it clean.
Never use a paper towel or regular cloth. It will scratch the prism. Rinse off saltwater with RO water. Any residual salt will cause inaccurate readings the next time you use the refractometer. Dropping or rough treatment can damage the internal ATC system or misalign the optics. Handle with care. Calibration once a month will ensure accurate readings. Digital Salt Meters Electronic salinity meters are also available.
Conclusions Refractometers were at one time too expensive for marine aquarists. Tags: specific gravity , sg , salt mix , salinity meter , salinity measure , salinity , refractometer , reef , ppt , nsw , natural seawater , mixing saltwater , milwaukee , icecap , hydrometer , hanna instruments , hanna , fowlr , digital refractometer , coral reef , coral.
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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. Other Tips on Using a Refractometer C lean the refractometer between each measurement using a soft, damp cloth.
Failure to wipe the prism can lead to inaccurate results and damage to the prism. Do not immerse the refractometer in water. If the refractometer looks foggy inside, water has entered it. You may or may not be able to dry it out without damaging the unit. Do not measure or clean it with abrasive or corrosive chemicals. If the scale is completely dark, you may not have added sample to it in the appropriate way.
If the scale is completely light, then the liquid's refractive index is above the refractometer's high end. Summary R efractometers are a quick and often accurate way to measure the salinity of reef aquarium water. Once checked to be sure that they were made correctly, they may provide years of service, providing they are not dropped onto a hard surface or into an aquarium.
As with many devices, however, you sometimes get what you pay for, and sometimes less. Very inexpensive refractometers can be prone to errors and may need to be checked in a solution matching seawater, not just pure freshwater.
Other methods of salinity determination are also quite suitable for reef aquarists. These include conductivity using electronic meters , and specific gravity using floating glass hydrometers.
Plastic swing arm hydrometers can be accurate, but seem to be more prone to inaccuracies than electronic meters and glass hydrometers.
In general, it is good to calibrate any device used with a seawater standard at least once to confirm its proper operation before relying on it to gauge the salinity in a reef aquarium. Refractometers and Salinity Measurement. Table 1. Index of Refraction of Various Materials. Index of Refraction. Figure 1. A plot of the relationship between the refractive index and the salinity of seawater. Figure 2. A plot of the relationship between the refractive index and the specific gravity of seawater in the range of interest to most reef aquarists.
The black circles represent data points for whole values of the salinity 33, ppt, 34 ppt, 35, ppt, etc. Table 2. The darker blue rows represent the range usually encountered in the open ocean.
Salinity ppt. Table 3. The error in salinity measurement via refractive index when magnesium is present at unusually high or low concentrations.
The darker blue row represents natural seawater. Magnesium ppm. Refractive Index. Predicted Salinity ppt. Figure 3. A schematic drawing of a typical hand held refractometer. Figure 4. The relationship between the real actual refractive index and the measured refractive index for a perfectly calibrated refractometer. Figure 5. The relationship between the refractive index and the salinity of seawater, showing that the usual point of calibration using pure freshwater is far from the range of measurement used in reef aquaria.
Figure 6. The relationship between the real actual refractive index and the measured refractive index for an incorrectly calibrated refractometer. This refractometer has an offset error, with all values reading higher than the actual value. Figure 7. Figure 8. Figure 9. The relationship between the real actual specific gravity and the measured specific gravity for a perfectly calibrated seawater refractometer green and an incorrectly calibrated seawater refractometer red.
The error in measuring the specific gravity of seawater with a real refractive index of 1. Figure The relationship between the real actual salinity and the measured salinity in ppt for a perfectly calibrated seawater refractometer green and an incorrectly calibrated seawater refractometer red.
The error in measuring the salinity of seawater with a real salinity of 35 ppt is indicated. The error can be corrected using a seawater standard. By turning the calibration screw until a seawater standard reads 1. In this case, accurate calibration can also be performed using freshwater.
By turning the calibration screw until a seawater standard reads 35 ppt, the red line moves onto the green line and the refractometer is properly calibrated. The relationship between the real actual refractive index and the measured refractive index for an incorrectly calibrated refractometer red and a perfectly calibrated refractometer green.
The error in reading refractive index values as far away as that of seawater can be significant, as shown. The refractometer of Figure 13 red has a slope error, with values far from the calibration point reading incorrectly. This type of error can only be corrected by calibrating with a solution with refractive index near to the expected measurement point.
The relationship between the real actual specific gravity and the measured specific gravity for an incorrectly calibrated seawater refractometer red and a perfectly calibrated seawater refractometer green.
This red refractometer has a slope error, with values far from the calibration point freshwater with a specific gravity of 1.
The amount of error in measuring seawater is indicated. This figure is an expansion of Figure 15 in the region of most interest to reef aquarists. The relationship between the real actual salinity and the measured salinity in ppt for an incorrectly calibrated seawater refractometer red and a perfectly calibrated seawater refractometer green. This red refractometer has a slope error, with values far from the calibration point freshwater with a salinity of 0 ppt reading higher than the actual value.
This figure is an expansion of Figure 17 in the region of most interest to reef aquarists. The refractometer of Figure 15 and 16 red has a slope error, with values far from the calibration point reading incorrectly.
In this figure it has been recalibrated with seawater and so is adequately accurate over the range of specific gravity from 1. This figure is an expansion of Figure 19 in the region of most interest to reef aquarists. The refractometer of Figure 17 and 18 red has a slope error, with values far from the calibration point reading incorrectly.
In this figure it has been recalibrated with seawater, and so is adequately accurate over the range of salinity of ppt despite the slope error.
This figure is an expansion of Figure 21 in the region of most interest to reef aquarists. The relationship between the real actual salinity and the measured salinity in ppt for a perfectly calibrated seawater refractometer green and a perfectly calibrated salt refractometer red.
This salt refractometer effectively has a significant slope error, with values far from the calibration point freshwater with a salinity of 0 ppt reading roughly 1.
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