Location
New Rochelle
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How do you calibrate your refractometer? With RO/DI water? I heard this and did it. Now the refractometer says my the specific gravity is 1.027? I have two hydrometers. One says 1.0235 and one says 1.023. Before I tried to calibrate the refractometer with RO/DI water, it said 1.024.

All tests done with the same sample.

If you use calibration solution and think that's how it should be done, where around here (Westchester/Bronx) can I pick some up?
 

EmilyT

Don't diss softies!
Location
CT
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you put RO/DI or distilled water on it and then with the small screwdriver that it hopefully comes with, adjust the line between the blue and white so that it goes down to zero.
 
Location
New Rochelle
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That's exactly what I did. Either my water IS at 1.027 and both hydrometers are off by just about the same amount, or... I don't know...

I can try it again, but it's not that hard to do and I don't think I F'ed it up...
 
Location
New Rochelle
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did you still get a reading of 1.024 for RO/DI or is it at zero now?


NO, No... Maybe I am confusing everyone...

Water in tank - hydrometers #1 = 1.0235
hydrometers #2 = 1.024
refractometer = 1.027

RO/DI Water - hydrometers #1 = 0.000
hydrometers #2 = 0.000
refractometer = 0.000

I never got a reading of 1.024 for RO/DI water on any of the instruments. I got a reading just below 0 on the refractometer with RO/DI water, and tuned it up to 0. That when this started happening.

 

jhart

Advanced Reefer
Location
Yonkers
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28   0   0
the way I calibrate my refractor is I boil water in a tea pot. wait for it to start to steam get a spoon over the steam the water droplets that build up on the spoon is distilled water, put three drops on the refracto, and your reading should be zero , if not get a little screw driver adjust horizon to zero... now you have a good starting point..
 

clownlover

Advanced Reefer
Location
brooklyn
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i saw this on premium aquatics:

*Refractometers are listed to be calibrated with RO/DI or Distilled water. There is some new information stating for best results you should use a Salinity Fluid like the American Marine Salinity Fluid. This will yield you much more accurate results.

How to calibrate with Salinity Fluid from American Marine: Take a couple drops and read your unit. You should read 1.0259 salinity or 35ppt. Adjust your unit to match one of these two numbers. Once you adjusted the refractometer is now fine tuned for saltwater salinity/ppt. If you read ro/di after calibration you will have a negative reading and that is completely normal, as the unit is fine tuned now for a saltwater tank.
 

Fragmented

Junior Member
Location
Selden, LI
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Some text from this link---

http://reefkeeping.com/issues/2006-12/rhf/index.php

Imperfect Refractometer Use: Scale Misunderstanding and Salt Refractometers

Refractometers can lead to incorrect readings in additional ways and, again, these issues abound for reef aquarists. One is that many refractometers are intended to measure sodium chloride solutions, not seawater. These are often called salt or brine refractometers. Despite the scale reading in ppt (?) or specific gravity, they are not intended to be used for seawater. Unfortunately, many refractometers used by aquarists fall into this category. In fact, very few refractometers used by hobbyists are true seawater refractometers.
Fortunately for aquarists, the differences between a salt refractometer and a seawater refractometer are not too large. A 35 ppt sodium chloride solution (3.5 weight percent sodium chloride in water) has the same refractive index as a 33.3 ppt seawater solution, so the error in using a perfectly calibrated salt refractometer is about 1.7 ppt, or 5% of the total salinity. This error is significant, in my opinion, but not usually enough to cause a reef aquarium to fail, assuming the aquarist has targeted an appropriate salinity in the first place. Figure 23 shows the relationship between a perfectly calibrated and accurate salt refractometer and a perfectly calibrated and accurate seawater refractometer when the units are reported in salinity. This figure shows the measured salinity reading for seawater being about 1.7 ppt higher than it really is.
Figure23.gif
Figure 23. 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 1.7 ppt higher than the actual value. Salt refractometers reading in salinity can be recalibrated using seawater to eliminate nearly all of this error (just as the refractometer in Figures 17 and 18 was recalibrated in seawater to give Figures 21 and 22).​

It turns out that this is a slope miscalibration in the sense that a perfectly made sodium chloride refractometer necessarily has a different relationship between refractive index and salinity than does seawater. This type of problem with a refractometer IS NOT at all corrected by calibrating it with pure freshwater. If you have this type of refractometer, and it was perfectly made and calibrated in freshwater, it will ALWAYS read seawater to be higher in salinity than it actually is (misreporting an actual 33.3 ppt to be 35 ppt).
Even more confusing, but perhaps a bit less of a problem in terms of the error's magnitude, salt refractometers sometimes read in specific gravity. But that value is specific gravity of a sodium chloride solution with the measured refractive index, not seawater with that refractive index. A sodium chloride solution with the same refractive index as 35 ppt seawater (which turns out to be 36.5 ppt sodium chloride) has a specific gravity matching 34.3 ppt seawater. So this type of refractometer, when perfectly calibrated, will read the specific gravity of 35 ppt seawater to be a bit low, at 1.0261 instead of about 1.0264. That error (reading 0.0003 or so too low) is, however, probably less than most reef aquarists are concerned with. Figure 24 shows the relationship between a perfectly calibrated and accurate salt refractometer and a perfectly calibrated and accurate seawater refractometer when the units are reported in specific gravity. This figure shows the measured salinity reading for seawater being about 0.0003 lower than it really is.
 

bad coffee

Inept at life.
Rating - 100%
27   0   0
I calibrated my refrato with RODI, and used it for about 3 years that way. I recently calibrated it with calibration fluid and it was 12ppt off. Yes, my refractometer said it was 47ppt instead of 35ppt. So when I was mixing up water to what I thought it was 35ppt, it was actually 23ppt (1.019!)

which would explain why my corals are dying...

B
 

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