Refractometer Calibration theory...question...

[BlastoLove]

If calibrating your refractometer with RO/DI is not accurate to pin point it to ZERO, what reading would RO/DI give you on the refractometer after calibrating it with the proper fluid??? Would the reading of ZERO TDS RO/DI be read at the same place on every properly calibrated refractomater???
:squigglemouth:

 

[Singlefin]

That's a good question. I think it does test out at 0. Maybe it's just not a controlled setting like the solution. There might be a little fluctuation in different people's Rodi. Not sure if everyone tests their tds before using Rodi. I've never had the solution and just use Rodi. It's fine. I switched back to nsw from salt mix and it always tests the same so I stopped testing my SW. I do have to calibrate my refractometer before each use.

 

[deboy69]

If I remember correctly when I tested it. Rodi read under zero when calibrated with calibration fluid

Sent from Earth

 

[markalot]

It all depends on the design of the refractometer. Mine reads +5 or so when calibrated with calibration fluid. I had a salinity accident due to calibration with RO/DI. I think this is where many people get into trouble. Someone with an unknown brand of refractometer calibrates with RODI and all is fine, they say so, then someone with another brand does it and nukes their tank because the slope error is different. The fluid is $7, just buy it, test it, make sure.

Here's a good article on the subject: Refractometers and Salinity Measurement by Randy Holmes-Farley - Reefkeeping.com

 

[Singlefin]

Very true. As with most things in this hobby, see what works for you and be consistent.

 

[jedimasterben]

Absolutely only calibrate with a stock solution of the salinity you aim to hit - 35ppt/53ms. If you calibrate with 0ppt RO/DI water, you are only accurate within a small range around 0ppt. Once you get into the 35ppt range (your targe), results can be skewed from 2ppt up to 5-6ppt.

 

[Jlobes]

+!

I always used RODI in the beginning, then I started to wonder about the calibration solutions. I ordered some up and got to testing. Seems, you get very different results...depending on the solution used to calibrate.

I didnt take notes at the time, but I remember thinking that, the amount of difference was quite substantial. And I would have to agree with Jedi^ it could be as different as 2-5ppt.

You dont use RODI to calibrate a PH probe or phosphate meter. So, just like a ph probe, use the proper and recommended solution for an accurate calibration.

Just my .02