Proper calibration of refractometer
- Thread starter kkil4life
- Start date
jdieck
New member
It is very important to understand that what we normaly buy are "Salinity" (brine) refractometers.
If you were to measure salt water rather than seawater then calibrating with RO/DI will be the way to go but we do not measure salt water but rather seawater and seawater has a diferent refractive index than salt water. This is the reason a calibration solution is used.
Using the pin point solution you should adjust the refractometer to read 35 parts per thousand or 1.0264 sg (not 1.025).
Once it is calibrated this way you SHOULD NOT recalibrate with RO/DI to zero or you will revert the calibration to measure salt water not sea water.
When calibrated with the solution at 1.0264 (35 PPT) the refractometer will read below 0 when measuring RO/DI unless that refractometer has been manufactured to measure seawater which there are not many out there.
For more detail on this please refer to the following article:
http://reefkeeping.com/issues/2006-12/rhf/index.php
If you were to measure salt water rather than seawater then calibrating with RO/DI will be the way to go but we do not measure salt water but rather seawater and seawater has a diferent refractive index than salt water. This is the reason a calibration solution is used.
Using the pin point solution you should adjust the refractometer to read 35 parts per thousand or 1.0264 sg (not 1.025).
Once it is calibrated this way you SHOULD NOT recalibrate with RO/DI to zero or you will revert the calibration to measure salt water not sea water.
When calibrated with the solution at 1.0264 (35 PPT) the refractometer will read below 0 when measuring RO/DI unless that refractometer has been manufactured to measure seawater which there are not many out there.
For more detail on this please refer to the following article:
http://reefkeeping.com/issues/2006-12/rhf/index.php
Jdieck, that was an interesting read.
So now I presume my refractometer is wrongly calibrated.
Do u know the difference in specific gravity in terms of actual measurement of 53ms solution n rodi
I mean If u calibrate with rodi n then use 53ms solution what specific gravity does the refractometer show you.
This way I can have my specific gravity somewhat right till I order the solution
ifisch, you have been of great help maybe you can try out the above as well
So now I presume my refractometer is wrongly calibrated.
Do u know the difference in specific gravity in terms of actual measurement of 53ms solution n rodi
I mean If u calibrate with rodi n then use 53ms solution what specific gravity does the refractometer show you.
This way I can have my specific gravity somewhat right till I order the solution
ifisch, you have been of great help maybe you can try out the above as well
sjfishguy
Active member
You should never calibrate with RO/DI. iFisch, if I understand you right, you calibrate with the pinpoint and then the DI right? That means you aren't calibrating with the pinpoint at all. Why would you move it with one solution and then move it with another? You dont calibrate a refractometer like a salinity MONITOR. Never use RO/DI to calibrate a seawater refractometer.
KK, you should not use the RO/DI at all, use the pinpoint and calibrate it to 35ppt. 35ppt=~1.026, but you should have both readings on your refractometer. Therefore, you are calibrating it so close to where we keep our tanks (1.025ish) you will have little to no error (as the article describes, but in a little more detail)
It is common to have RO/DI read less than 1.000 after PROPER calibration with pinpoint. Each refractometer is different, that is why you need to calibrate it, so therefore no one can say, just set it to X with DI and that will be 35ppt with pinpoint. If it were that easy you wouldn't need to calibrate it.
KK, you should not use the RO/DI at all, use the pinpoint and calibrate it to 35ppt. 35ppt=~1.026, but you should have both readings on your refractometer. Therefore, you are calibrating it so close to where we keep our tanks (1.025ish) you will have little to no error (as the article describes, but in a little more detail)
It is common to have RO/DI read less than 1.000 after PROPER calibration with pinpoint. Each refractometer is different, that is why you need to calibrate it, so therefore no one can say, just set it to X with DI and that will be 35ppt with pinpoint. If it were that easy you wouldn't need to calibrate it.
jdieck
New member
You can wait until you get the solution, if I remember well the difference is not as significant to cause any issues (like about 0.01). One reason why I recommend to wait is that as sjfish mentions, all refractometers are different, coincidentally during tests, some of the cheapo refractometers were behaving as if they were made for sea water rather than salt water.
Salty Irishman
Premium Member
Just checked mine with calibration fluid made from this article http://reefkeeping.com/issues/2006-12/rhf/index.php and then checked with RO/DI. Both readings were were 35 & 0 respectively. IMO the error is not enough to concern your self with so long as things remain constant, of course this is with my refractometer. My advice, don't panic, and when you can check both ways (calibration solution & RO/DI) and then adjust accordingly.
jdieck
New member
After that article and after several people tried it there was concluded that unless you use good scales and labware for measurement, it was very difficult to get it right specially considering that the amount of moisture in the salt can vary the measurements, just try to do it as accurately as possible.
iFisch
New member
No. When I FIRST got my unit, I used RODI to calibrate to 1.000. Then I bought the Pinpoint solution. Put a few drops on the refractometer, and adjusted the unit to 1.025, since my unit was a little bit off (too high).
I use either solution to check my calibration, which holds pretty good. A solid month is about all I get before I need to recalibrate, which is usually just a point or two off by that time.
I could never get the DIY calibration fluid just right. I am "measuring cup impaired". I use the 53ms solution, and my refract is way off with RODI. Some may be accurate at both ends. but dont assume it will be. I see no reason to use RODI for calibration since you are using the instrument to measure salt water, not fresh water.
jdieck
New member
Yes, when using the pin point solution, the calibration shall be made to 1.0264 or it's equivalent 35 ppt.
This does not mean that you can not later on mix your salt water at 1.025 it just means that the 1.025 reading will be more accurate when calibrating to 1.0264 with the pin point than when calibrationg 1.0 using RO/DI.
sjfishguy
Active member
iFisch, seems your unit is pretty good to begin with then. You are lucky. Most people (nearly all actually) when they calibrate their unit with the pinpoint to 35ppt, the 0 level is WAY off. I found this out the hardway, before anyone knew about the pinpoint solution. When the pinpoint solution was first discuss to calibrate refractometers a few years ago, I went out and got it. After calibration my tank was actually at 1.022! When I brought up my tank to 1.025 it was amazing how much better my corals looked.
iFisch
New member
Yeah, um, that's not happening with the refractometers I've seen. There's a line for 1.025. I calibrate to the next line right above 1.025.
Since I don't have an electronic salinity meter, I can't "pinpoint" the exact salinity to the thousandths.
If my reading is 1.025 or one line above it, I'm fine.
My current chemistry problem as well as the calibration of my refractometer is making me think what if indeed my salinity is lower than it showing me.
Even if I order the pinpoint 53ms solution tomorrow i wouldn't get it unt a few weeks I guess
can I go collect water from the beach and calibrate it to that at 35 ppt for the time being till o get my solution?
Im not trying to be cheap or anything it's just that I'm trying to get the best done I can without having to wait for the solution.
What specific gravity should the water from the beach show me?
Even if I order the pinpoint 53ms solution tomorrow i wouldn't get it unt a few weeks I guess
can I go collect water from the beach and calibrate it to that at 35 ppt for the time being till o get my solution?
Im not trying to be cheap or anything it's just that I'm trying to get the best done I can without having to wait for the solution.
What specific gravity should the water from the beach show me?
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