refractometer calibration

[Nano]

Originally Posted by sphelps

This is a point of the thread to eliminate the myths involved with refractometer calibration. Straight tap water reads zero on my refractometer, which was just proven accurate.

really?
but water quality varies where ever you go, so personally wouldn't use tap water for my refractometer
especially considering the poor water quality we have in Wetaskiwin

[Coralgurl]

The refractometer is for salinity. Try it and see what it says then compare to you RO, if the numbers are the same, then I would say either is fine for calibrating it. If you get different numbers then just use your ro.

[Snappy]

It should be able to test for both salinity & specific gravity.
I believe that the proper water temp should also be part of the equation for calibrating. Please correct me if I am wrong.

[sphelps]

Originally Posted by Nano

really?
but water quality varies where ever you go, so personally wouldn't use tap water for my refractometer
especially considering the poor water quality we have in Wetaskiwin

Yes really, my tap water isn't great here either, sitting at around 300ppm. However the point wasn't to tell you to use tap water but rather your RO water is perfectly fine for calibrating. At the end of the day do you feel best with but you are wasting your time bringing your refractometer to a LFS for calibrating. They will either use RO water or a calibration fluid, however unless the calibration fluid is new (more likely been sitting around for long time) you probably run more risk with that being contaminated.

As for temperature ideally what you use to calibrate should be close to your tank temp as far I as know, however IME this makes little difference as well as long as it's pretty close, ie room temp is fine.

I encourage anyone to try calibrating their refractometer with proper solution and comparing the results for themselves. I only only posted this to prevent the need for others to try such an experiment and put to rest the myth of inaccurate refractometers. Now I'm not saying there ins't error involved however the errors we are talking about are in the ppm range while our equipment measures in the ppt range with is 1000 times greater. You simply can't measure that kind of error with our refractometers nor can you even calibrate the device that accurately anyway.

[Zoaelite]

Originally Posted by sphelps

Yes really, my tap water isn't great here either, sitting at around 300ppm. However the point wasn't to tell you to use tap water but rather your RO water is perfectly fine for calibrating. At the end of the day do you feel best with but you are wasting your time bringing your refractometer to a LFS for calibrating. They will either use RO water or a calibration fluid, however unless the calibration fluid is new (more likely been sitting around for long time) you probably run more risk with that being contaminated.

As for temperature ideally what you use to calibrate should be close to your tank temp as far I as know, however IME this makes little difference as well as long as it's pretty close, ie room temp is fine.

I encourage anyone to try calibrating their refractometer with proper solution and comparing the results for themselves. I only only posted this to prevent the need for others to try such an experiment and put to rest the myth of inaccurate refractometers. Now I'm not saying there ins't error involved however the errors we are talking about are in the ppm range while our equipment measures in the ppt range with is 1000 times greater. You simply can't measure that kind of error with our refractometers nor can you even calibrate the device that accurately anyway.

I'm on board with calibrating with with RO water but in my person experience a cold refractometer can give an incorrect reading.
Colder instrument---> Salt water cooled---> Density drops---> Incorrect reading. That being said everything I have read says the amount is almost negligible, where's Kien when you need a science experiment done!!

[sphelps]

Yeah density obviously decreases with temperature but at a rate of less than one tenth of a percent per 10 degrees C. So if you're close it really won't make a difference. Not to say you should use boiling or close to freezing temp water to calibrate but using say 21C water to calibrate for a tank running at 24C really won't make a detectable difference.

To give an idea, 4C RO water from my fridge reads about 0.5ppt on my refractometer, just barely over the zero line. And that's a pretty significant temperature difference.

[Zoaelite]

I'm not near my tank, anyway you can do the same with salt water and see if that changes the reading a measurable amount?

[sphelps]

Originally Posted by Zoaelite

I'm not near my tank, anyway you can do the same with salt water and see if that changes the reading a measurable amount?

I'll put the calibration fluid in the fridge and post later

[rayjay]

If you have a seawater refractometer then calibration with water should provide a good reading at normal salt water ranges. However, it is still recommended that one use calibration fluid.
If you have a salt water refractometer (NaCl) which is most common in the hobby, there will be an error at normal salt water ranges if calibrated with water.
Randy Holmes-Farley on Refractometers and Salinity

[sphelps]

Originally Posted by Zoaelite

I'm not near my tank, anyway you can do the same with salt water and see if that changes the reading a measurable amount?

1.026 Calibration fluid reads 1.027 at 4 degrees C