HELP! Refractometer Calibration Fluid Verification.

Tokalosh

Well-Known Member
Is there a way to make sure your calibration fluid for your refractometer is still good?
I calibrated my refractometer with RO to zero and then took a reading of my calibration fluid and got 45 PPT.

Is this reading something to go by and does the fluid have a shelf life?

I’ve had mine for two years now but was starting to wonder if it needed to be replaced anytime soon.


Thanks

Tok
 

chipmunkofdoom2

Well-Known Member
If you don't trust your calibration fluid, try making your own and see how it compares to the store-bought stuff. From Randy Holmes-Farley:

[Speaking about 35ppt sea water]: This concentration roughly corresponds to ¼ cup (73.1 g) of Morton's Iodized Salt dissolved into two liters (2000 g) of water (giving very slightly more than 2 L of total volume).

(Full article here.)

The readings of any refractometer can change over time. Theoretically, as long as you recalibrate every so often with a known good solution, you should always be getting solid readings. Unless of course the refractometer is damaged and changes readings between calibrations.

If you're worried about your refractometer being damaged or broken, I'd first confirm that your solution is good (try the home made solution as mentioned above, or take it to a LFS and ask them to help with some of their water). Then, after you get your hands on some good calibration fluid and you've successfully calibrated your refractometer to 35ppt, recheck it every week. If you see the value changing, that could indicate a problem: refractometers shouldn't be falling out of calibration weekly. If, however, your readings are stable over the next few weeks, I'd continue to use it. Just be sure to re-check the calibration every few weeks.

As an aside, most refractometers recommend calibrating to zero with fresh water, but I'm not a huge fan of that method. It doesn't really matter if the refractometer is accurate at 0 ppt because you're not using it to measure 0 ppt water. You're using it to measure 35 ppt water.
 

StirCrayzy

Well-Known Member
Good reminder to check mine, been 5+ yrs...
I don't the difference calibration to zero is much simpler to verify than 35.
Everyone has immediate access to zero with RODI, without concocting some mixture manually.
If zero is accurate, 35 should be accurate by the same degree of accuracy that zero reads. This isn't rocket science, no need to over complicate things. I was upset to find that I had to use special fluid to calibrate mine, but I did when I first got it, and haven't since. Because of what C.O.D. just stated. First you have to calibrate the calibration fluid... Duh.
Not raggin on you C.O.D. good to see you back posting. Your contributions are missed on the LED scene.
 

PSU4ME

JoePa lives on!!!
Staff member
PREMIUM
Doing it this way takes the reading way below 0 PPT.
Ok well that's good then, we know it's not the refractometer now. If try the recommendation above or just buy new solution. If the new solution lines up with the "ro zero" then just toss the old fluid. Odds are with the high reading you've had some water evap out
 

Tokalosh

Well-Known Member
44 PPT = 1.0133 SG, OMG Ho did I not pick this up sooner!!!!

Thanks for all the input guy, very much appreciated. I took my water to my LFS and asked them to chek it. The results were that my readings with my calibration fluid were +10 over. Turns out I've slowly been killing off my tank and none the wiser. The water I had mixed up to do a water change with is 45PPT, I'm so glad I did not do a water change today.

It just goes to show that you can't take the eye off the ball for one second in this hobby!

Tok
 

PSU4ME

JoePa lives on!!!
Staff member
PREMIUM
I replace mine every year because it's so hard to trust. Another thing I do, I got very standard in my water changes, to the point the I could mix very close to the 1.026 range by eyeballing how much salt I put in. If I would do that and the reading was high or low I calibrated. Just a safety precaution.
 

StirCrayzy

Well-Known Member
Even if you don't calibrate at zero, it is so simple to throw some Rodi on the glass just to see how close it is.
I still can't believe I don't think to check more often.

I eyeball my salt too, but keep meaning to try by weight to check consistency
 
Top