How do you properly calibrate a Refractometer?

[tbone28]

I received my Marine Depot meter and Pinpoint 53ms calibration fluid today :rollface:

Queston about calibrating it:

The refractometer's instructions say to calibrate it at a room temperature of 68 degrees.

The Pinpoint calibration solution reads:

"53ms +/-1% @77 degrees.

Did you guys calibrate it at a room temp of 68 or 77 degrees? Or does the temp even matter?

Thanks

Edit: I just calibrated the meter at a room temp of 68 degrees. I calibrated the meter with both the Pinpoint solution and with the RO/DI water that I make. The calibrate at 0.03 difference! Should there be such a big gap?

Am I doing something wrong with the calibration?

[Percula9]

It should be self compensating for temp. I would calibrate it to the calibration solution. Check it against distilled water instead.

[PSam]

The 53ms solution has been, more recently, recommended over DI water. Check the chemistry forum, they were commenting on it a couple days ago.

[woz52]

I am a chemist and what we have always done to "calibrate" a refract is to use the water source that you are using to make your salt water. ie ro/di, distilled, tap. you then could make a standard solution using your makeup water to determine if the readings are correct. I have never heard of calibrating your refract with a calibration solution. The most important thing with a refract is setting your zero with your makeup water.. as far as temperature. the effects are irrelevant unless you are first boiling or freezing your water before testing it with the refract. Almost all good refracts will compensate for temperature except for the extremes.

[bertoni]

The PinPoint solution is the best approach. It has an ionic content similar to seawater, and should measure about 1.0264 at 25 C on a true seawater refractometer, of which there are none in the generally hobbyist price range. RO-DI doesn't work in all cases for various reasons:

http://reefkeeping.com/issues/2006-12/rhf/index.php

I suspect the PinPoint solution is just artificial saltwater adjusted using a high-accuracy and high-precision conductivity meter.

[tbone28]

Good article. Thanks! I figured out what my problem was. I was using the Pinpoint solution, but calibrating it to 1.00! After calibrating it to 1.0264 (35ppt), the difference between calibrating with Pinpoint versus RODI water is only 0.001.

Thanks for your help!

[bertoni]

You're welcome! Good luck!