Refractometer Qs

[rdmpe]

Ahh - I hadn't thought of that!

The pinpoint PH monitor I have has a chart that states that 53.0 mS reading is equiv. to 1.026 salinity. So are you saying that this fluid may generate the correct conductivity reading, but might not generate the correct refractive index? So the fluid conductivity may be right at 53.0 mS but that may be due to some compound other than salt? I wonder if we can get any info on this from Pinpoint...

 

[rdmpe]

Well, after reading some more on this, it seems that sewater RI is not exactly the same as NaCl RI for the same PPT content. Here's something I found

... 99.99 % of all refractrs, we would use in the hobby, are calibrated to NaCl Salinity. Salinity does not mean seawater salinity, it could be KCl, NaCl Salinity etc.. It is the salinity of any "salt". Seawater Salinity is not the same as NaCl Salinity or KCl Salinity, each has its own RI (Refractive Index). In other words, a 35 ppt NaCl RI is not the same as a 35 ppt RI for KCl or Seawater. In order to calibrate a refract to NSW you would want a sample that had the same RI as seawater. So, that would be a sample of seawater that is know to be 35 ppt or to mathematically calculate a salinity using another salt that would = NSW. Such is the case with the 3.65 % NaCl, which = NSW @ 3.5 % Salinity. ...

So does the DIY refractometer calibration fluid recipe account for this? And I assume that if I did cook some of that fluid up, it might not read 53.0 mS on my conductivity meter right?

 

[rdmpe]

This is the recipe I was referring to
http://www.reefkeeping.com/issues/2004-06/rhf/index.php

Edit - I see that it does account for the different RI of NaCl. So now I need to make some of this up and see how it compares to the calibration fluid for the pinpoint monitor. Maybe my refractometer is off! maybe a good thing I use the refractometer for the "change water" salinity rather than the main tank salinity...

Always learning stuff around here...

 

[dela]

So is that fluid appropriate for a refractometer?

 

[Randy Holmes-Farley]

The pinpoint PH monitor I have has a chart that states that 53.0 mS reading is equiv. to 1.026 salinity. So are you saying that this fluid may generate the correct conductivity reading, but might not generate the correct refractive index? So the fluid conductivity may be right at 53.0 mS but that may be due to some compound other than salt? I wonder if we can get any info on this from Pinpoint...

Correct. If it were seawater, then it would be fine, but it isn't. It is likely NaCl or KCl, and those will be different. In my article on a DIY standard, one can see how they are different for NaCl.

So is that fluid appropriate for a refractometer?

Which fluid? In my article, I give three, one for each method.

 

[jrw]

While this is interesting and educational, are we not served well with our refractometer if it is always consistent. This allows us to maintain consistent with a tank that is doing well? For me the advantage of the refrac over the swing arm hydrometer is its consistency.

 

[Randy Holmes-Farley]

But aren't you served better if it is accurate? It is not hard to verify.

 

[dela]

Randy,

Sorry for the vague question. I meant to ask, is the linked commercial solution appropriate for refractometer calibration? I would be OK with spending the extra $3 for a highly accurate refractometer. That was the whole point of the purchase.

The reason I ask is that the solution is meant for the pinpoint salinity monitor, which probably operates on conductivity rather than refraction.

While this is interesting and educational, are we not served well with our refractometer if it is always consistent.

What if it's consistently wrong? How would that be any good?

 

[Randy Holmes-Farley]

Sorry for the vague question. I meant to ask, is the linked commercial solution appropriate for refractometer calibration?

No, it isn't. It is for a conductivity meter.

 

[obybobie]

lol you people and your refractometers so
critical i use a frickin redsea hydro meter, make sure all the bubbles are off and its damn close to a refractometer tested at the fish store up agains a refract

 

[Randy Holmes-Farley]

make sure all the bubbles are off and its damn close to a refractometer tested at the fish store up agains a refract

I wonder if their refractometer was accurate.

You can test your hydrometer with the DIY standards too.

 

[dela]

That's what I was afraid of.

Thanks

 

[rdmpe]

I prefer the frackin hydro meter. Much better than the frickin hydro meter.