Refractometer calibration

[korbynlehr]

I just got a new refractometer and the instructions say to calibrate it with distilled water. Does anyone know if I can substitute RO water for the distilled?

[Randy Holmes-Farley]

RO water is usually as good as distilled for this, and RO/DI is equally as good as distilled, but none of these may really be adequate.

Check this thread:
http://www.reefcentral.com/forums/showthread.php?s=&threadid=953605

[korbynlehr]

Randy,
Can you provide a link for your calibration fluid recipe? Also do I use RO/DI water for your recipe?

[korbynlehr]

Is this a correct recipe to get the calibration fluid? How long does this need to mix or sit before using?

To produce a 3.714 weight percent sodium chloride solution, dissolve 1 teaspoon (6.20 grams) of Morton's Iodized Salt in 161 mL (161 g) of fresh water (making a total volume of about 163 mL after dissolution of the salt).

[Randy Holmes-Farley]

The mix described above is for a hydrometer, not a refractometer. As soon as it is fully dissolved and clear, it can be used.

You can buy a commercial standard for not too much from American Marine/Pinpoint.

My DIY recipes for all methods of salinity measurement are here:

Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.htm

[korbynlehr]

Okay I am looking at 3 different calibration fluids. There is a 4,7 and a 10. Which should be used? Also how often should I check the calibration?

[korbynlehr]

NEVERMIND I am an idiot!
I obviously was looking at the PH calibration fluids.

[jag1979]

you are looking at ph calibration fluid I think

[korbynlehr]

Okay I am really feeling like an idiot. Can someone cut and paste the exact recipe for Randy's calibration fluid that I need to use for my refractometer?

I WOULD REALLY APPRECIATE IT!!!

[old salty]

One last question here as I am going to make a cal solution today when I get to work.


3.65g of salt into 96.35ml of water is what I am intending to mix. When I place this on my refractometer, where do I set the blue line (on the meter) so that the calibration is correct?

[doesheya]

And the answer is?

[Randy Holmes-Farley]

Reef Aquarium Salinity: Homemade Calibration Standards
http://reefkeeping.com/issues/2004-06/rhf/index.htm

[old salty]

Ever have one of those days where you just do not comprehend what you are reading? I call those, "Fridays". Anyhow, I did this today and set the blue line to 35ppt. When I check DI water afterwards, I get 0. Kind of strange; maybe I got the good one.

[Randy Holmes-Farley]

For what seems to me to be hard to understand, some folks have found that the refractometers read the salt solution incorrectly when calibrated to RO/DI, but then when calibrated with the salt standard, they still read RO/DI water OK.

More often, if you are off in one direction you will be off in the other direction.

In any case, you seem all set then. :)

[IndyReefMan]

Randy--

It seems that these refractometers are all made by the same company (as reported in an earlier thread). If so many people are reporting them to be inaccurate when calibrated with RO/DI water, then it seems unusual to me that a few people are reporting them to be accurate. What do you think?

[Randy Holmes-Farley]

I don't know why some seem more or less accurate than others.

[doesheya]

the 2L of water + 1/4 cup + 1 teaspoon salt

Is this a correct recipe for the calibration of my refractometer?

[korbynlehr]

is this 1/4 and 1 teaspoon mortons ionized salt to 2 liters water?

[Billybeau1]

I personally had a heck of a time mixing Randy's homemade calibration recipe properly. What I finally did was purchase a few bottles of Pinpoints 53.0mS calibration fluid from American Marine and calibrated my refractometer to that standard. Perfect. And cheap too.

[doesheya]

<a href=showthread.php?s=&postid=8526060#post8526060 target=_blank>Originally posted</a> by korbynlehr
is this 1/4 and 1 teaspoon mortons ionized salt to 2 liters water?

So did u figure it out?

[korbynlehr]

Nope not yet just ordered the pinpoint calibration fluid so hopefully it will be here in the next day or two or three.

[doesheya]

<a href=showthread.php?s=&postid=8537139#post8537139 target=_blank>Originally posted</a> by korbynlehr
Nope not yet just ordered the pinpoint calibration fluid so hopefully it will be here in the next day or two or three.

Are u sure that is what u need?

[Billybeau1]

I tested the pinpoint calibration fluid against my lab grade hydrometer and it was perfect. My refract read it at 35 ppt. I'd say its a good check and balance.

[korbynlehr]

Thanks for the info Billy.

[Billybeau1]

:thumbsup: