Calibrate your refractometer with calibration fluid!

[jennm]

Specific gravity in the ocean can vary.

Having said that, calibrating a refractometer with 35 PPT solution will keep you close enough to the acceptable range, versus using RO/DI water to 'tare' it.

Not all refractometers are created equal. I have one I've had for over 15 years, that I used to use multiple times a day (in my shop) and when I checked it with solution it never really varied. Then I've had others, new out of the box, that needed to be tweaked every time - they didn't hold a calibration well.

Specific gravity can and does vary in the ocean so as long as you're close and consistent, things will be OK - but as some have mentioned, if something goes wonky and your SG is way low or way high, that causes problems.

This is a situation where common sense should prevail.

I'm not sure if LFS will calibrate with solution for you - I did when I had my place. It's a good idea to check it regularly, and yes, calibrating with a solution with a known specific gravity is best.

Jenn

 

[kwajtrader]

One more data point: I recently picked up a second refractometer from another member and it came with a bottle of calibration fluid from the same manufacturer as one I recently purchased. The old bottle of 35ppm fluid read 1ppm lower than the new fluid. In other words, After I calibrated both refractometers to the new bottle of fluid at 35ppm, the old bottle of fluid read 34ppm on both refractometers. That seems counter intuitive. You would think over time evaporation would cause the concentration of the older bottle to rise. Puzzling...

 

[bobz]

OK so this thread has completely freaked me out and now I am going online to order some calibration fluid. Thanks guys.

 

[lmm1967]

Check your instructions too. Mine is a Red Sea and when I went back and checked they stated to calibrate to zero with RO and let it sit for a couple minutes and it will auto adjust for temp as well. I have confirmed if I use cold water (65 degrees or so) the readings are different if I check immediately versus wait a minute.




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[k3nnyp]

Calibrating my ATC refractometer with RO water and then with calibration fluid showed a dramatic difference in values. I checked my tank water after each to determine the difference. 1.020 vs 1.026

 

[wade]

k3nnyP;1107843 wrote: Calibrating my ATC refractometer with RO water and then with calibration fluid showed a dramatic difference in values. I checked my tank water after each to determine the difference. 1.020 vs 1.026

Did you take any readings on the RO water? RO can have some degree of conductivity associated with it. That can skew your results. As can not waiting for temperature compensation (the droplet equilibrates to the device temp) to occur. That said, I still wouldn't be surprised to see a difference, but that seems very far apart.

 

[outdrsyguy1]

i loved schwaggs idea to buy a bottle of calibration fluid at each meeting and everyone there can bring there devices. sounds like a cool perk to me!

 

[bcavalli]

That is a great idea and we'll make it happen.

 

[Adam]

The idea is good but I find my ATC refractometer needs slight adjustments much more frequently than would be suffice from monthly meetings. Buying bottle of fluid or making your own from Randy Holmes-Farley's instructions isn't that expensive. I'd rather know my new batches are mixed right than take the chance that the refractometer is drifting.

 

[xilez]

anit77;1108031 wrote: The idea is good but I find my ATC refractometer needs slight adjustments much more frequently than would be suffice from monthly meetings. Buying bottle of fluid or making your own from Randy Holmes-Farley's instructions isn't that expensive. I'd rather know my new batches are mixed right than take the chance that the refractometer is drifting.

Link to Randys recipe?

 

[Adam]

If anyone hasn't read up on the multitude of articles Randy has posted/published I highly recommend looking him up. I don't think any one person has helped the reefing community with water chemistry more than he has. He's has his own sub forum on R2R. (Used to be on RC too)

Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.php">http://reefkeeping.com/issues/2004-06/rhf/index.php</a>

Refractometers and Salinity Measurement
[IMG]http://reefkeeping.com/issues/2006-12/rhf/">http://reefkeeping.com/issues/2006-12/rhf/</a>

And a more recent one.
DIY Salinity calibration solutions
[IMG]http://www.reef2reef.com/threads/diy-salinity-calibration-solutions.220052/">http://www.reef2reef.com/threads/diy-salinity-calibration-solutions.220052/</a>

 

[k3nnyp]

wade;1107846 wrote: Did you take any readings on the RO water? RO can have some degree of conductivity associated with it. That can skew your results. As can not waiting for temperature compensation (the droplet equilibrates to the device temp) to occur. That said, I still wouldn't be surprised to see a difference, but that seems very far apart.

No I didn't but that's a great idea. I'll give it a try next time I'm calibrating.