Refractometer Calibration??
- Thread starter kb0vhy
- Start date
If your readings are off after using R0/DI water then you should suspect contamination of the RO/DI you are using, or the lineararity of the Refractometer. Depending on the precision of the Refractometer at the High and Low ends of the measurement scale, your accuracy may drop off. At what reading are you off .002 - .003. if it is at 1.5000...who cares.
Whether you calibrate using RO/DI or Pinpoint Solution or or any other standard. Pure H20 (RO/DI) should read 0.000.
Whether you calibrate using RO/DI or Pinpoint Solution or or any other standard. Pure H20 (RO/DI) should read 0.000.
DrBDC
Active member
It is the same issue as using pH calibration solution at 4 and 7 for your tank. It will not be as accurate as using 7 and 10. Nothing wrong with my unit or water. It has been discussed thouroughly in the chemistry forum and most are finding the refractometers off by even up to .004 and .005. The slope is usually staying the same but if you calibrate with a standardized solution, you will find the ro/di is either slightly lower or higher than the 0 mark due to an improper offset. Unless of course you are using a 2-300 dollar refractometer.
Here is an article on refractometers and calibrations:
http://reefkeeping.com/issues/2006-12/rhf/index.php
Here is a few threads discussing it:
http://www.reefcentral.com/forums/s...d=988417&highlight=refractometer+and+pinpoint
http://www.reefcentral.com/forums/s...d=953605&highlight=refractometer+and+pinpoint
http://www.reefcentral.com/forums/s...=1027872&highlight=refractometer+and+pinpoint
Here is an article on refractometers and calibrations:
http://reefkeeping.com/issues/2006-12/rhf/index.php
Here is a few threads discussing it:
http://www.reefcentral.com/forums/s...d=988417&highlight=refractometer+and+pinpoint
http://www.reefcentral.com/forums/s...d=953605&highlight=refractometer+and+pinpoint
http://www.reefcentral.com/forums/s...=1027872&highlight=refractometer+and+pinpoint
That is basically what I am saying DrBDC. I’m not disagreeing on your statements; it is just that it a little impractical for every day reef use. I have one of the nicer refractometers that I ordered from a lab supply company. I have read all of the articles you linked and I have 13 years of clinical lab experience and routinely calibrate clinical instruments. I am by no means an expert, but I know a little on this type of issue.
It's all about linearity and the precision of the instrument you using. I have used a known, lab grade standard to calibrate my refractometer. After about 20 or so calibrations it didn’t budge and I just used pure H2O to check it after that. While I totally agree that you may find that your refractometer is off .004-.005 what you are comparing it to? If you don't use a standard that is fresh then you can falsely calibrate it anyways (pinpoint usually is in individual packs so not an issue)
You can use a $500 standard to calibrate your $80 refractometer, but what are you actually doing? While you used the PH calibration example you’re comparing a 2 point calibration to a single point calibration you do with a refractometer (apples to oranges). If the refractometer is accurate to +/- .005 then you probably should calibrate it once using a standard, and then measure pure H2O and make that reading your calibration point (kinda a 2 pt cal/check). In addition, if you if use the more expensive calibration solution, and calibrate it to 1.025 (precision) then you may still be off when measuring salinities other than that measurement (accuracy), but only at smaller amounts.
You’re also quoting the extreme amount that they have found refractometers off (like the $20 versions). So basically it comes down to how anal you are. If you suspect your refractometer to be off, then by all means check it with some standard to make yourself feel better. Pure H20 is fine for reef purposes for most refractometers.
While using pure H2O to calibrate your refractometer may only calibrate it for readings of 0.0000 it should be pretty darn close when measuring at other salinities.
The best cost/benefit solution would be to cal it once with a standard, then take the reading of RO/DI H2O to cal to, and from there out use H2O.
…basically don't use an electron microscope to find your car keys.
It's all about linearity and the precision of the instrument you using. I have used a known, lab grade standard to calibrate my refractometer. After about 20 or so calibrations it didn’t budge and I just used pure H2O to check it after that. While I totally agree that you may find that your refractometer is off .004-.005 what you are comparing it to? If you don't use a standard that is fresh then you can falsely calibrate it anyways (pinpoint usually is in individual packs so not an issue)
You can use a $500 standard to calibrate your $80 refractometer, but what are you actually doing? While you used the PH calibration example you’re comparing a 2 point calibration to a single point calibration you do with a refractometer (apples to oranges). If the refractometer is accurate to +/- .005 then you probably should calibrate it once using a standard, and then measure pure H2O and make that reading your calibration point (kinda a 2 pt cal/check). In addition, if you if use the more expensive calibration solution, and calibrate it to 1.025 (precision) then you may still be off when measuring salinities other than that measurement (accuracy), but only at smaller amounts.
You’re also quoting the extreme amount that they have found refractometers off (like the $20 versions). So basically it comes down to how anal you are. If you suspect your refractometer to be off, then by all means check it with some standard to make yourself feel better. Pure H20 is fine for reef purposes for most refractometers.
While using pure H2O to calibrate your refractometer may only calibrate it for readings of 0.0000 it should be pretty darn close when measuring at other salinities.
The best cost/benefit solution would be to cal it once with a standard, then take the reading of RO/DI H2O to cal to, and from there out use H2O.
…basically don't use an electron microscope to find your car keys.
DrBDC
Active member
I wouldn't worry about getting a 500 dollar calibration either! :lol: I'd just guess by taste before that!
The pinpoint bottle of 53 mv solution is 1.0265 and runs about 3 bucks a bottle. Or maybe it was 5 bucks and 2 for 8 or something close. There was a batch IIRC that there was an issue with but Robert (I think that's his name) from Amercan Marine and Randy were talking and it was taken care of. I tried the salt in a 2 liter method and it is too much of a PITA and too hard to verify the accuracy.
I think most of the refractometer are close enough too. Most the calibration issues have been on the usual RHS-10ATC's and similar ones which aren't cheap but they're under 100.
But the difference between 1.0265 and 1.0235 is a considerable difference. I scrapped it all and went with the salinity conductivity meter anyway so it's moot to me anymore. I keep it around just in case. I actually still have a floating hydrometer around here somewhere. From what I understand, a quality lab version of the floating hydrometer (not the ones we see at the LFS or petco) are also fairly cheap and pretty darn good too.
The pinpoint bottle of 53 mv solution is 1.0265 and runs about 3 bucks a bottle. Or maybe it was 5 bucks and 2 for 8 or something close. There was a batch IIRC that there was an issue with but Robert (I think that's his name) from Amercan Marine and Randy were talking and it was taken care of. I tried the salt in a 2 liter method and it is too much of a PITA and too hard to verify the accuracy.
I think most of the refractometer are close enough too. Most the calibration issues have been on the usual RHS-10ATC's and similar ones which aren't cheap but they're under 100.
But the difference between 1.0265 and 1.0235 is a considerable difference. I scrapped it all and went with the salinity conductivity meter anyway so it's moot to me anymore. I keep it around just in case. I actually still have a floating hydrometer around here somewhere. From what I understand, a quality lab version of the floating hydrometer (not the ones we see at the LFS or petco) are also fairly cheap and pretty darn good too.
