Rookie looking for some answers

[Kasey]

Got my refractometer today:

http://www.drsfostersmith.com/product/p ... catid=9957

My Coral Life swing arm reads 1.022, my refractometer reads 1.024.

I threw out the Instant Ocean one....

 

[Mthompson]

I would suggest making some calibration standards for you refractometer. Here is a link to some pretty clear and simple directions on how to make some at home:

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

Or, you could always buy some online somewhere. By using these you can be certain that you are getting a correct reading. With refractometers you just put the standard in and adjust the calibration knob so that the SG of the refractometer matches the SG of the standard.

 

[Kasey]

Thanks for the article, very informative.

What about just buying a jug of already mixed saltwater and measuring that?

 

[PezJunkie]

Thanks for the article, very informative.

What about just buying a jug of already mixed saltwater and measuring that?

Seems to me that using that method will only tell you if your measuring device matches somebody else's measuring device... not necessarily if it is accurate or not.

 

[Kasey]

I meant a premixed container from the store.

Your device should match the label on the carton.

 

[Mthompson]

The problem with that is that you can't be sure what the SG is supposed to be. Mixing inherently contains errors or deviations.

This is exactly what a standard is for. If you make the standard from pure H20 and add the correct amount of salt, you can be certain it has a KNOWN SG value. Since you know what the standard solution SG is, then you can calibrate your equipment to read that SG when the standard solution is in it.

I'd bet that most schools (especially a high school) in your area would have accurate scales and/or graduated cylinders you could borrow for a few seconds.

For a refractometer, all you need to make is about 100mL of standard (which is 250+ calibrations if the container is well sealed). The article doesn't mention that water weighs less as temperature increases; pure water at 75F weighs 99.44% of the same amount at 39.2F.

Here are the numbers I calculated for 75F ambient temperature to make a 35 PSU or 1.0264 SG standard solution.

Weight (g) Sodium Chloride - 3.63 g
Weight (g) pure water - 95.81 g
Volume of standard - 99.44 mL

So, just set everything out for a few hours and then measure and mix. Viola! Homemade SG standard solution!

 

[gdubb]

Thanks for the links and the info.