Refractometer Issues

[Brian Kim]

Hi guys, so I am having issues with my refractometer and was hoping someone could help me out with my unit being off by 0.05, which is a lot.
Took it to one of the lfs to have it calibrated using their RO water and when I brought it back home and tested with my RO water, it was 0.05 below 0.
It didn't really make sense so I took it to another lfs and calibrated using their RO water. Came back home and tested it with my RO water and it was again 0.05 below 0. I then tested my tap water and it was exactly 0.05 below 0.
The only thing I can think of at this moment is the temperature affecting the measurement since my RO holding tank is in my garage and it's been around 30-40 here in NYC during morning hours.
BTW, neither store had 53.0 mS fluid

 

[Jlobes]

the problem is you are using RO to calibrate. try using a confirmed 35ppt calibration solution, as this is a better set point for your calibration. check this link, it might help:
http://reef2reef.com/threads/refractometer-make-sure-its-calibrated.224558/#post-2599520

 

[Randy Holmes-Farley Verified Community Expert]

OK, first let's clarify. It cannot be off by 0.05, because 1.025 would be reading as 1.075 (which probably isn't even on the scale).

So do you mean that 1.0250 reads as 1.0255? (how accurately can you read your refractometer? can you easily and reproducibly distinguish 1.0250 from 1.0255?)

Is it an ATC refractometer (Automatic Temperature Compensation)?

 

[Randy Holmes-Farley Verified Community Expert]

The only thing I can think of at this moment is the temperature affecting the measurement since my RO holding tank is in my garage and it's been around 30-40 here in NYC during morning hours.
BTW, neither store had 53.0 mS fluid

OK, now I see the 30-40 deg F. Even an ATC refractometer cannot compensate that much. Bring some water inside and let it warm to room or tank temp, before calibration.

And when you can, get or make a 35 ppt standard.

 

[Brian Kim]

OK, first let's clarify. It cannot be off by 0.05, because 1.025 would be reading as 1.075 (which probably isn't even on the scale).

So do you mean that 1.0250 reads as 1.0255? (how accurately can you read your refractometer? can you easily and reproducibly distinguish 1.0250 from 1.0255?)

Is it an ATC refractometer (Automatic Temperature Compensation)?

Sorry...I meant to say 0.005, 1.025 would read 1.030
Yes it's an ATC

 

[Brian Kim]

I have also added my test result on the other post in regards to refractometers, created by Dekon.
Anyways, it seems that temperature was the problem for the major fluctuation.

 

[Randy Holmes-Farley Verified Community Expert]

That makes sense.

Happy Reefing.

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, my revised Refractometer article has just published in the December issues of ReefEdition here at Reef2Reef:

Refractometers And Salinity Measurement
http://www.reefedition.com/refractometers-salinity-measurement/

 

[Brian Kim]

FWIW, my revised Refractometer article has just published in the December issues of ReefEdition here at Reef2Reef:

Refractometers And Salinity Measurement
http://www.reefedition.com/refractometers-salinity-measurement/

Very informative article

 

[Randy Holmes-Farley Verified Community Expert]

Very informative article

Thanks, Brian.

 

[Brian Kim]

so to add to the story, I received my 53.0 mS tester after this post and it came early in the morning when temperature here in NYC was in the upper 40's (Can you believe I had to pay $14.99 for calibrated saltwater lol) and immediately proceeded to test my refractomer and can confirm cold temperature will have an impact of exactly if not close to 0.005