Refractometer Calibration

Most of us are using a refractometer calibrated for Sodium Chloride (NaCl) as opposed to NSW including myself. This has always posed a problem because these refractometers are .0015 too low in SG when calibrated using RO/DI water or distilled. I've always calibrated to zero and just mentally made the adjustment.

The other option is to use a 53 mS solution and then calibrate to 35 ppt/1.0265 SG as opposed to zero and make no adjustment whatsoever. You can also make your own solution. Reef Aquarium Salinity: Homemade Calibration Standards by Randy Holmes-Farley - Reefkeeping.com

The reason I'm interested in this poll is because Randy Holmes-Farley and Boomer have been testing a lot of refracts recently in preparation for an article and they've found many as far off as .003 SG. A properly made refractometer should only be off .0015 SG. That's spooky. Imagine thinking you're at 1.026 when you're really at 1.023.

Please pick a choice for question number 1....What type of refractometer do you have?
Please pick a choice for question number 2.....How do you calibrate?

 

Well, I can see that this poll isn't going to work. Option 1 on question 2 was supposed to be, "I calibrate to zero with RO/DI water".

If any mod's know how to fix this, please do so. Until this happens, please use option 1 if you use RO/DI water or distilled water.

 

(I fixed it. I am looking into the permission issue.)

 

You da man Matt!!!

Thanks

C

 

No prob.
Looks like you need some more votes so I am bumping this.

 

I calibrate to zero with RO/DI water

 

Yeah, it shocks me. I was expecting more discussion.

Most people think that their refractometers are accurate when 99.9% of them I've seen in the hobby are low by .0015 SG brand new right out of the box because they are calibrated to NaCl as opposed to NSW.

 

Interesting, when I set up my current system in June, I purchased a refractometer from the LFS. The same one that came out with a truck load of RO/DI premixed water to get us up and running. There was no discussion about different types of refractometers, just a brief training session on using, read, cleaning, and & calabration checks (using RO/DI).

After reading the instructions that came with it, the MFG confirms that the refractometer is calabrated with RO/DI.

So, every week when I run out some RO/DI for the make up tank, I do a quick 'cal' check. I have had to adjust it only once since purchase, and that was just a very small tweek.

So, do I have a NaCl or NSW refractometer , I don't know.....

 

More than likely, it's NaCl. I only know of two NSW refracts that are affordable enough for hobbiests.

Refractometers
National Microscope.com - New and Used Microscopes, Refractometers and Supplies

The most common model that hobbiests are using is the RHS-10atc model which is produced by two separate companies. (The second company copied the first company's model number). If you have this model (from either company), it is calibrated to NaCl and not NSW.

 

Here's where it get's tricky. You can calibrate a NSW refractometer with RO/DI water and it will be 100% accurate. The instructions for NaCl refracts also say to calibrate with RO/DI water or Distilled water and those will be inaccurate by .0015 SG by doing so.

There are refractometers for alcohol, blood, urine, honey, you name it.