Calibrating Refractometer

What is the proper environment to calibrate a refractometer? I have calibrated mine using fresh RODI in the same temperature room as the RODI water used. I go and test the tank water, after letting it acclimate to the meter's temp, and get .002 of a difference on the high side as the swing arm hydrometer. It's an ATC meter, and a nice one at that. Not sure which to believe or if I'm actually going through the calibration steps correctly. Thanks for looking

 

You will need a calibration liquid to do it correctly.Also keep in mind the light source should always be the same .If you calibrate it in sunlight it will show a slightly different number when then used under a lightbulb or fluorescent fixture.Always calibrate and use the refractometer using the same light source.

 

http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=18717
Temperature is important as this too can alter results.It is always best to be sure the temperatures are the same when measuring.Some refractometers will compensate for temperature differences but its best if they are at least close.

 

Ok Thanks. What about the temperature of the calibration fluid? Does it need to be at a specific temp in order to accurately calibrate?

 

Technically but like I said most refractometers will compensate for temperature to some degree.
Love your Dachshund.They are my all time favorites.Did you catch the weiner dog commercial during the superbowl?Awesome!!lol

 

This is a fantastic read on refractometers.
http://reefkeeping.com/issues/2006-12/rhf/

 

Yup, sure did! Thanks for the link

 

Agree with vinny, get some calibration fluid. ATC will pretty much adjust it's self with temp. I have the red sea refractometer and when I calibrate it with the fluid I wait 45 seconds before I make any adjustments. When I'm checking my water after calibration I wait about 20 seconds. Using the same light source will ensure accuracy, I use the led daylight bulb in the kitchen.

 

And I've GOT to add-

Unfortunately- you often have to check the calibration fluids accduracy as well.

We had a workshop last year in our club, everyone brought their hydrometers, refractometers,
I brought my calibration fluid. ( I did this when others had inaccurate cal. fluids. previously)

I mean why even buy a cal. fluid- like $9 for some salt water when you can't even trust it!!?

My cal. fluid was consistently high on 3 of those higher tech 'Milwaukee' instruments!!
It was about 37- when it was sold as 35.

I'm not sure what the age of it should have an effect, mine was a few years old, always kept tightly capped.
But from some H2O molecules leaking out of a small bottle as gasses- that would raise it some.

NOw when I use that same cal fluid, I calibrate it to 37. I need to check it again and see if it went up more.

Moral of the story- although we buy a cal. fluid and want to trust it......

 

After I almost ruined my tank with salinity above scale I calibrate with RO water+30ppt+35ppt and then I measure the water.
And the plan is to change those fluids rather often (half year interval) or until I see some discrepancies between the 3.