Refractometer Question

[packisbak1]

I am convinced that my hydrometer does not work (it gives me a different reading every time). I am therefore considering a refractometer. Does anyone use the refractometer being sold at Dr Fosters for $41.99? Is this the best value you can find? Will I need to buy calibration fluid? Thanks.http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=9957&Nty=1&Ntx=mode+matchallpartial&Ntk=All&pc=1&N=0&Ntt=refractometer&Np=1

[reef_doug]

It looks like the same one I have and the price is right.

Yes, it's highly recommended to get the Pinpoint 53ms Calibration fluid to calibrate it to 35 ppt. The Pinpoint fluid is much more accurate than calibrating with RO/DI at the bottom of the salinity scale.

[Billybeau1]

I ditto Reef Doug.

Those refracts are just fine as long as you keep them calibrated with the 53mS fluid.

Once you use it, you won't know why you didn't buy it before. :D

[KevChem]

OK - I'm a chemist and I'm a bit confused about this issue :rollface:

According to this article:

http://www.reefkeeping.com/issues/2004-06/rhf/index.php

A 53mS/cm conductivity standard is made as 3.24% KCl or 3.29% NaCl solution. If you look at the refractometer section of the article (Table 2), a 3.29% NaCl solution has an equivalent salinity of less than 32 and a refractive index of less than 1.3388 and a specific gravity (Table 5) of less than 1.0243.

So buying a 53mS/cm Conductivity standard and using it to calibrate a refractometer to a specific gravity of 1.0264 seems like it won't work.

Please help me understand.

Kevin

[Percula9]

The calibrating fluid has a salinity of 35 ppt. If your refrac is calibrated it should read out at 35ppt. If not then turn the calibration knob until it reads 35ppt.

[Randy Holmes-Farley]

Please help me understand.

Sure.

You do not use a 53 mS/cm sodium or potassium chloride solution to calibrate a refractometer.

The Pinpoint 53 mS/cm is not such a solution, but is a seawater mimic solution, so it matches seawater at 35 ppt in all of specific gravity, refractive index, and conductivity.

In my DIY standard where we do use sodium chloride solutions,

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

we use 3.65 weight percent sodium chloride to match the refractive index of 35 ppt seawater. It does not have a conductivity of 53 mS/cm. You use 3.29 weight percent sodium chloride for that.

Make sense? :)

[KevChem]

<a href=showthread.php?s=&postid=11855143#post11855143 target=_blank>Originally posted</a> by Randy Holmes-Farley
Please help me understand.

Sure.

You do not use a 53 mS/cm sodium or potassium chloride solution to calibrate a refractometer.

The Pinpoint 53 mS/cm is not such a solution, but is a seawater mimic solution, so it matches seawater at 35 ppt in all of specific gravity, refractive index, and conductivity.

In my DIY standard where we do use sodium chloride solutions,

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

we use 3.65 weight percent sodium chloride to match the refractive index of 35 ppt seawater. It does not have a conductivity of 53 mS/cm. You use 3.29 weight percent sodium chloride for that.

Make sense? :)

It does now. I tried to find that commercial solution (another thread linked to a DrF&S page), but couldn't, hence the confusion.

Thanks!

Kevin

[Randy Holmes-Farley]

You're welcome.

I just wish more folks knew enough to ask such detailed questions! :D

Happy Reefing. :)

[Billybeau1]

<a href=showthread.php?s=&postid=11855230#post11855230 target=_blank>Originally posted</a> by KevChem
It does now. I tried to find that commercial solution (another thread linked to a DrF&S page), but couldn't, hence the confusion.

Thanks!

Kevin

You can get the Pinpoint 53mS calibration fluid at "The Filter Guys"

They are a sponsor here. :)

[EvilE]

<a href=showthread.php?s=&postid=11855942#post11855942 target=_blank>Originally posted</a> by Billybeau1
You can get the Pinpoint 53mS calibration fluid at "The Filter Guys"

They are a sponsor here. :) yeah for $11 shipping...:mad2: I found it MUCH cheaper on Ebay--same exact solution!;) *although it is good to support the sponsors! I try to do that as much as possible, just couldn't bring myself to pay $11 shipping on a 2 ounce product.

[asm481]

The pinpoint solution is available from dfs. Just hard to find.

[Randy Holmes-Farley]

It is also available directly from American Marine (Pinpoint):

http://www.americanmarineusa.com/accessories.html

[asm481]

I mentioned it by DFS because you are looking at their refractometer. I did a bit of digging and here it is.
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=18717