Refractometer Calibration Fluid Off?

[BradVol]

I have a refractometer and 2 bottles of calibration solution. I calibrated it to 35 with one and tested the other and got 33. What should I do?

I could split the difference, buy a third bottle, go with the newer bottle, etc but I'm surprised the two are off that much. One is Brightwell and one is Fritz, both 335 ppt.

 

[KStatefan]

Make you own solution

 

[Garf]

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

 

[Randy Holmes-Farley Verified Community Expert]

One should be careful that not all 35 ppt calibration fluids are suitable for all types of devices. The article above has different solutions for refractometers, conductivity meters, and hydrometers.

to be honest, neither of those two brands mentioned has high esteem from me in terms of chemistry understanding.

 

[trainbob]

What brands of calibration fluid would you recommend other than your dyi solution or are they all bad

 

[Geebs19]

Would just using 0TDS water to 0 work instead of solution? Thats what I have always been told to do.

 

[PeterEde]

What brands of calibration fluid would you recommend other than your dyi solution or are they all bad

Or just get the Hanna Salinity checker.
That's what I just did.
And discovered my refractometer was pretty close. My Hanna showed my tank at 35ppt at 26deg C

 

[trainbob]

Most people suggest to use a calibration fluid at the recommended measurement you will strive for

 

[trainbob]

I am waiting for the Milwaukee digital refractormeter supposed to be coming Thursday which should still use calibration fluid. I was responding to Randy Holmes Farley saying that the two fluids mentioned weren’t highly thought of

 

[Sean Clark]

I am waiting for the Milwaukee digital refractormeter supposed to be coming Thursday which should still use calibration fluid. I was responding to Randy Holmes Farley saying that the two fluids mentioned weren’t highly thought of

These use rodi or distilled for calibration. I think the "issue" people take with this method is that it is calibrated far from its intended use. 1.00 vs 1.026 for example but that doesn't really hold any weight when you consider the percentage of deviation from the measured solution to the known calibration solution is less that 0.03%.

 

[vic5hands]

Easy use RODI water calibration to Zero

 

[trainbob]

The Milwaukee comes with both distilled water and calibration fluid. I am asking because it seems that so many people have issues with calibration fluid being different. Just wondering if there is a better fluid out there. Even different LFS have issues. One store close to me has an Aqua spinner but it doesn’t test salinity

 

[BradVol]

I've made some progress on this. I bought a Milwaukee MA887 on ebay for $48 (score!) and it showed up today. I cleaned it and zeroed it and did a few tests. My tank tested at 34 ppt, which is the target. My older Brightwell 35ppt calibration fluid tested at 37ppt. The newer Fritz tested at 35ppt. So far everything lines up pretty well. I have a Tropic Marin hydrometer coming tomorrow that should provide a real standard, provided I can measure the temperature accurately. I haven't checked yet how much a degree or two affects the hydrometer readings.

My initial reaction is that the MA887 is really nice and seems like it will be consistent if I follow all the recommendations: clean and zero before each test, let sample sit one minute before testing, cover to prevent light from getting into the measurement.

Short of something new throwing everything out of whack I think I'll have a quite good process to make sure things are within a reasonable range going forward.

 

[trainbob]

Good buy on EBay when I looked all they had was a new one for almost $150

 

[Randy Holmes-Farley Verified Community Expert]

Would just using 0TDS water to 0 work instead of solution? Thats what I have always been told to do.

If you have a true seawater refractometer, and it is made and calibrated perfectly, 0 ppm TDS is fine for calibration. But that list of requirements is not easily obtained in a cheap hobby refractometer.

If you have a brine refractometer (as are often sold to hobbyists), and it is made and calibrated perfectly using 0 ppm TDS water, it will necessarily read incorrectly at 35 ppt because seawater and brine (NaCl) have a different relationship between refractive index and salinity. It is a dirty little secret of hobby suppliers, some of whom probably don't even know it themselves.

If you have any type of refractometer, made perfectly or not, and oyu calibrate it correctly for 35 ppt seawater, it will correctly read 35 ppt seawater.

hence the desire (IMO) to use a 35 ppt standard.

 

[Randy Holmes-Farley Verified Community Expert]

Easy use RODI water calibration to Zero

Sometimes that is OK, and sometimes it is inherently inaccurate, as I note above.

 

[Randy Holmes-Farley Verified Community Expert]

These use rodi or distilled for calibration. I think the "issue" people take with this method is that it is calibrated far from its intended use. 1.00 vs 1.026 for example but that doesn't really hold any weight when you consider the percentage of deviation from the measured solution to the known calibration solution is less that 0.03%.

Two issues with that.

First, that's not the reason (at least not the main reason).

Second, you cannot use the leading 1 in that calculation. The difference between sg = 1.025 and 1.026 is 3.8% change in salinity. The difference between sg = 1.000 and sg = 1.026 is a 100% difference in salinity.

 

[Sean Clark]

Two issues with that.

First, that's not the reason (at least not the main reason).

Second, you cannot use the leading 1 in that calculation. The difference between sg = 1.025 and 1.026 is 3.8% change in salinity. The difference between sg = 1.000 and sg = 1.026 is a 100% difference in salinity.

Yep, I definitely missed the mark on that math. I wasn't thinking straight. Thanks.