Refractometer calibration

[jdpeters]

I have a refractometer that seems to need to be calibrated at every use, has anyone experienced that before? Also how important is the temperature of the solution or even the water I’m testing?

 

[penfold2]

Yes, I had one that would change by a couple points no matter how often I calibrated it. I exchanged it for a new one and the problem disappeared.

As for temperature, most refractometers are auto temperature correcting. If you just let the sample sit for 30 seconds, you'll get an accurate measurement.

 

[Reefer1978]

Cheaper refractometers tend to be that way

 

[BriDroid]

I had a really, really cheap one that wouldn’t hold a calibration at all. In the trash it went and I got a nicer one that holds calibration great. I still check it with a 35ppt reference solution once a month.

 

[redfishbluefish]

I had a similar issue 6 or 7 years ago and found that the little door portion wasn't closing completely and all it needed was a little lubrication. Have a post about here:

Lubricate Your Refractometer

A little WD40 fixed my issue!

 

[jdpeters]

Yes, I had one that would change by a couple points no matter how often I calibrated it. I exchanged it for a new one and the problem disappeared.

As for temperature, most refractometers are auto temperature correcting. If you just let the sample sit for 30 seconds, you'll get an accurate measurement.

I will try to let the sample sit for a moment then. The frequent calibration isn’t that annoying I just want to make sure it’s showing an accurate reading.

Cheaper refractometers tend to be that way

noted. As long as I’m getting an accurate reading I’m gonna role with it

I had a similar issue 6 or 7 years ago and found that the little door portion wasn't closing completely and all it needed was a little lubrication. Have a post about here:

Lubricate Your Refractometer

A little WD40 fixed my issue!

I will look into this thank you.

 

[skiergd011013]

I had a really, really cheap one that wouldn’t hold a calibration at all. In the trash it went and I got a nicer one that holds calibration great. I still check it with a 35ppt reference solution once a month.

Be careful with the references if you bought them and didnt make them yourself. I tried the one from BRS and the continuum reagents one from amazon. They were both dead wrong, very low. I made my own with randys instructions to get a true 1.026 reference( which is how i discovered the store bought ones are crap). I bet a lot of people using store bought references are running their salinitys way off.

 

[BriDroid]

Be careful with the references if you bought them and didnt make them yourself. I tried the one from BRS and the continuum reagents one from amazon. They were both dead wrong, very low. I made my own with randys instructions to get a true 1.026 reference( which is how i discovered the store bought ones are crap). I bet a lot of people using store bought references are running their salinitys way off.

I learned that from one I bought from Amazon. I use Randy’s recipe to make my own now! Cheaper and easier with a small gram scale!

 

[exnisstech]

I'm going on 9 years with my cheap ATC from Amazon. Mine rarely needs calibrated tho I check it before each use with Randy's calibration fluid.

 

[Freenow54]

Yes, I had one that would change by a couple points no matter how often I calibrated it. I exchanged it for a new one and the problem disappeared.

As for temperature, most refractometers are auto temperature correcting. If you just let the sample sit for 30 seconds, you'll get an accurate measurement.

On a suggestion I just received Brightwell calibration solution I have had the same refractometer for years and never checked it. It was perfect but worth the effort

 

[GSPClown94]

I've noticed that if temperature of the refractometer is different than when it was calibrated then it often needs to be recalibrated at its new temperature or brought back to the temperature it was originally calibrated at to get an accurate reading.

 

[Randy Holmes-Farley Verified Community Expert]

I've noticed that if temperature of the refractometer is different than when it was calibrated then it often needs to be recalibrated at its new temperature or brought back to the temperature it was originally calibrated at to get an accurate reading.

If it is an ATC (automatic temperature compensation) refractometer, then neither the calibration nor the measurement temperatures should matter, as long as you are within the ATC range. If there is a difference, then the ATC is not working properly. :)

 

[GSPClown94]

If it is an ATC (automatic temperature compensation) refractometer, then neither the calibration nor the measurement temperatures should matter, as long as you are within the ATC range. If there is a difference, then the ATC is not working properly. :)

It is an ATC refractometer and has behaved like this since it was brand new. My old one also behaved the same. It's possible the refractometer is just junk.

 

[Freenow54]

It is an ATC refractometer and has behaved like this since it was brand new. My old one also behaved the same. It's possible the refractometer is just junk.

Mine is VERTEX. I remember reading a post a few years ago where some people did not rinse them after use and let them get corroded. I never understood that

 

[punchy7080]

I check that mine reports 0.000 with ro/di water. Is that a fair way to calibrate and if not, why not?

 

[BriDroid]

I this one from Amazon. For a cheapie, it has been really good. It holds calibration extremely well. I check it with Randy’s DIY calibration fluid. I’ve been very happy with it.

 

[Garf]

I check that mine reports 0.000 with ro/di water. Is that a fair way to calibrate and if not, why not?

Only if your refractometer is designed for that, even then it's always better to calibrate at, or near, your target measurement. Bare in mind that refractometers can claim you can calibrate with RODI, when in fact they should not be.

 

[Randy Holmes-Farley Verified Community Expert]

I check that mine reports 0.000 with ro/di water. Is that a fair way to calibrate and if not, why not?

I explain here why that is often not the case, even if manufacturers claim it, and it is also typically not best practice to calibrate anything far from the measurement value.

https://www.reefedition.com/refractometers-salinity-measurement/

 

[punchy7080]

I explain here why that is often not the case, even if manufacturers claim it, and it is also typically not best practice to calibrate anything far from the measurement value.

https://www.reefedition.com/refractometers-salinity-measurement/

I hadn’t seen your DIY recipe. Seems simple enough and something I can trust to get consistent results. I assume you specifically mention Coke bottles because they allow for the correct volume I’ of water? Should they be filled all the way to the top then?

Thank you!

 

[Miami Reef]

True seawater refractometers, like the digital Milwaukee, need to be calibrated with freshwater.