Calibration of Refractometer

noj3333

New member
I just bought some calibration fluid, as I've been trying to be more precise with my tank's chemistry.

I do have a few very quick questions:

The fluid I purchased is "NaCl in DI H20". I believe that's just Sodium Chloride (salt) in Deionized Water, am I correct there?

The fluid I purchased is 35.0ppt, and it says it's 1.0247 g/cm3. Does specific gravity have a unit of measure with it? I calibrated my refractometer to 1.026 (Per Randys Holmes-Falrley's tank parameters of sg=1.026 and 35 ppt), but the 1.0247 g/cm had me a little worried, should that be the point I calibrate it to?

Thanks for any help here.
 

jason2459

Premium Member
You should have two scales on your refractometer. I would calibrate it to the specific gravity of 1.0264 or salinity of 35ppt.

What brand of calibration solution did you get?
 

noj3333

New member
I bought it on-line (from e-bay). The company was National Industrial Supply. I'll calibrate my refractometer to 1.0264.
Thanks!
 

noj3333

New member
Yup, that's it. I hope it's a reliable source. I don't have any local source to check with as everyone (including LFS) uses RO/DI water to calibrate.
I will say the packaging was very professional, so I hope that is an indication of the overall product...
 

dendrite

New member
I'm not sure that I would over analyze or over complicated the issue, especially down to the fourth decimal place, which is beyond my visual resolution. Most of us probably use ro/di water to zero set the instrument, and there are other variables involved such as temperature both of the instrument and the water tested. I think the critical element is consistency whether at 1.025 , or 1.026 or 1.0264.
 

jason2459

Premium Member
I'm not sure that I would over analyze or over complicated the issue, especially down to the fourth decimal place, which is beyond my visual resolution. Most of us probably use ro/di water to zero set the instrument, and there are other variables involved such as temperature both of the instrument and the water tested. I think the critical element is consistency whether at 1.025 , or 1.026 or 1.0264.

1.026 is fine but the refractometer should have an easy to distinguish 35ppt mark to calibrate to with the calibration solution.

I would not suggest calibrating most refractometers to 0. If you have to make your own.

http://www.reefkeeping.com/issues/2004-06/rhf/
 

noj3333

New member
I agree, I just set my refractometer to 1.026 / 35ppt (or the closest I could get to that). My main concern, and reason for calibration, was that I wanted to make sure I was in a good, safe range.
 

jason2459

Premium Member
35 ppt of a sodium chloride solution will not be correct for 1.026 SG seawater. This article might help:

http://reefkeeping.com/issues/2004-06/rhf/index.htm

It'll read about 1.025 or so on a properly calibrated seawater refractometer. I'd probably spring for something like the PinPoint solution, which is intended for saltwater measurement.

I agree with going with pinpoint as it's had a long track record. Though I did just recently get a bad bottle that didn't read properly. The wording on NIS's site sounds right but if the solution doesn't match the verbiage it doesn't matter.
 
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