How often do you calibrate...

[Syris]

your refractometer? Just curious becasue I have had mine for almost 2yrs now and only calibrated it once when I first got it

I dont know why but I just never thought of doing it again until this weekend when I was doing a water change. And I found it was off by .005 so instead of my tank being 1.025 it was actually at 1.020, doogh!

 

[wrassefan]

I've checked quarterly and it hasn't strayed

 

[Jim Tansey]

OK I need to do mine.................... Very close not worth recalibrating, been 6 mo or more since I checked.

Jim

 

[gordonzoo]

I put ro/di on it to check 0. is there another solution we can use to check the top end?

 

[nunofs]

There's a special salinity/condutivity calibration solution: http://marinedepot.com/md_viewItem.asp?idproduct=NS5393

Nuno

 

[this is me]

Every 3 months or so I check my refractometer with RO/DI. I never had to calibrate it since its always at 0

 

[Randy Holmes-Farley]

I wouldn't use that fluid for calibrating anything except a conductivity meter. It may not match other properties to NSW.

 

[nunofs]

Thanks for the clarification, Randy. I had read there's a conversion factor/table between conductivity and salinity, but maybe that only applies to the digital conductivity meters.

What would you suggest as an alternative to DI/distilled water to calibrate a refractometer?

Nuno

 

[Randy Holmes-Farley]

The conversion depends on what the fluid is. If that 53 mS/cm standard was real seawater, or close to it, it would be fine for any device. But since it is probably some other salt, like sodium chloride or potassium chloride, then it can match NSW conductivity, but not match NSW refractive index or specific gravity.

I provide some DIY standards in this article, and you can also buy them:

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


Also, if you have multiple devices, you can use that commercial standard to calibrate a conductivity meter, and then measure tank water, and use the tank water reading to calibrate a refractometer or hydrometer.

 

[nunofs]

Randy: thanks for the explanation, that makes sense. I took a quick look at the article, it's bookmarked to read in full later, there's lots of interesting info in there.

Nuno