Public Service Announcement: Calibrate your refractometer. Stop ignoring the basics.

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ScottB

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Good golly you are on it. Doh!


Never mind folks. Nothing to see here. Darn thing has been correct for 6 years running, it is just the USER that needs recalibrating. I will confirm this in a bit, but this would account for what I was seeing yesterday.

Thanks @piranhaman00
I keep user manuals. Sadly, I don't always READ them. From the STX3 manual:

"Open the daylight plate and apply one or two drops of distilled water on to the surface of the prism. Hold the prism at an angle close to parallel with the floor so the distilled water will not run off of the prism."
 
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RobW

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VEEGEE should be calibrated with rodi water not reference solution unless you make your own solution. Popular reference solutions are at 20C and Veegee atc to 15C
i'm always wondering what is the best calibration solution. I've done it with ro/di. I always mix my saltwater batches the same. my tank seems to be at 1.025 every single time that I check it. I've never had a wandering value. I just have a 35.00 refractometer from Petco (Imagitarium) I think its called. everything seems well in the tank so... there's that.
 

AquaBiomics

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Regardless what the instructions say, refractometers should always and only be calibrated with 35 ppt calibration solution. The laws of physics and basic lab procedures don't change just because the guy who wrote the manual for a particular brand had a misunderstanding about how these things work.
 

RobW

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Using freshwater to calibrate it makes no sense. Use a solution near or at the measurement value.
ok, well what solution is the best? i've read reviews and they all seem to be all over the place. just didn't want to go get something that would throw everything off and end up upsetting the tank.
 
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davidcalgary29

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ok, well what solution is the best? i've read reviews and they all seem to be all over the place. just didn't want to go get something that would throw everything off and end up upsetting the tank.
Be sure to make sure your calibration solution is well-shaken if you do use one from a commercial source! I calibrate my refractometer every week (it does drift), and I was getting strange readings until I agitated the solution.
 
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ScottB

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Regardless what the instructions say, refractometers should always and only be calibrated with 35 ppt calibration solution. The laws of physics and basic lab procedures don't change just because the guy who wrote the manual for a particular brand had a misunderstanding about how these things work.
Your reply leaves me with considerable angst given the enormous SPREAD between the outcomes of the two calibration methods.

Using RODI calibration, my tank reads 1.026
Using 35 PPT solution from Reagents by Continuum Aquatics, my tank reads 1.020-
Using LFS generic ATC refractometer with 35PPT calibration reads 1.025+

Oh the previous joy of blissful ignorance.
 

piranhaman00

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i'm always wondering what is the best calibration solution. I've done it with ro/di. I always mix my saltwater batches the same. my tank seems to be at 1.025 every single time that I check it. I've never had a wandering value. I just have a 35.00 refractometer from Petco (Imagitarium) I think its called. everything seems well in the tank so... there's that.
See below :)
Regardless what the instructions say, refractometers should always and only be calibrated with 35 ppt calibration solution. The laws of physics and basic lab procedures don't change just because the guy who wrote the manual for a particular brand had a misunderstanding about how these things work.
Wrong
Using freshwater to calibrate it makes no sense. Use a solution near or at the measurement value.
Wrong.
ok, well what solution is the best? i've read reviews and they all seem to be all over the place. just didn't want to go get something that would throw everything off and end up upsetting the tank.

The “correct” solution depends on the refractometer. Cheap common ones that around 25$ need to use 35ppt solution. This is because they are inaccurate and you need to calibrate as close as possible. Keep in mind ALL refractometers with ATC are ATC to 20C. Those standards are 35ppt at 25C. 35ppt is not 35ppt at 20C so you are all ready adding some inaccuracy.

The VeeGee is very high precision. It uses rodi to calibrate because RODI is 0ppt at 20C. VeeGee, like all other refractometers is atc to 20C. This provides perfect calibration.

You can get away with using cheap and calibration fluid no doubt, I am simply stating what is the best method for calibrating refractometers.

Again if you are using a cheap refractometers do not use rodi, they are not precise enough to hold calibration through the entire range up to 35ppt.
 

piranhaman00

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Your reply leaves me with considerable angst given the enormous SPREAD between the outcomes of the two calibration methods.

Using RODI calibration, my tank reads 1.026
Using 35 PPT solution from Reagents by Continuum Aquatics, my tank reads 1.020-
Using LFS generic ATC refractometer with 35PPT calibration reads 1.025+

Oh the previous joy of blissful ignorance.
you should double check with a conductivity meter. They are more accurate that using refractometers anyhow :) although I trust my Veegee more .

I use Veegee refractometers and Hanna conductivity
 
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ScottB

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This is ideal. Making your own solution at 35ppt and calibrating I agree with. You are correct here :)
I don't understand. How is this different than using a reference solution when it comes to a VeeGee? Or are you speaking to non-VeeGee refractometers?
 

piranhaman00

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I don't understand. How is this different than using a reference solution when it comes to a VeeGee? Or are you speaking to non-VeeGee refractometers?

Standards you purchase online are not made from saltwater. They are just fluids with a certain refractive index, and again at different temps then refracts are compensating too
 

piranhaman00

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I don't understand. How is this different than using a reference solution when it comes to a VeeGee? Or are you speaking to non-VeeGee refractometers?
You can calibrate a Veegee with a standard but it’s just not as accurate as using rodi, or like this person mentioned making your own standard. But that’s only as good as you make the standard and it why I prefer rodi as it’s always 0ppt and can’t be screwed up:)
 
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