Calibrating a Refractometer with 53.0 ms fluid

[Carlo]

Without getting overly complicated PSU in our environment can be thought of as the same thing as salinity.

If it was only at 36% that wasn't to bad. I've seen much, much worse. One unnamed member tested out at 39% with the 35%/53mS solution with his refractometer at my house.

Some refractometers calibrate better then others with RO/DI water and of course you need good RO/DI water or it throws things off. It's worth the $3 for peace of mind when so many elements ride on proper salinity.

Carlo

 

[Phyl]

But isn't it more the delta rather than the number (obviously within reason) that really matters? Does it matter so much if it is off .0007 in one direction or the other if the delta over time is reasonable?

Did you happen to check the RO/DI against the solution when you calibrated said refractometer?

While PSU is the same as salinity, it represents parts per THOUSAND, not parts per hundred (percent).

 

[Carlo]

Nope doesn't matter at all. On a reef the salinity is constantly changing.

For example in the Fiji/Tonga areas the salinity can be anywhere from 33%-35% depending on runoff, currents, etc. Lagoons are even worse.

Carlo

 

[Boomer]

Let me clarify a couple of things. First, that % on the right side of a refract is not 35 % or 37 % it is 3.5 % and 3.7 %. Seawater is a 3.5 % solution = 35 ppt, also written 35 o/oo, or 35,000 ppm. Some have the % replaced with ppt. Second, many of these cheap Chinese refracts have been shown to be ***off from 0 ppt to + 4 ppt*** or 1.0264(35 ppt ) - 1.0205 (27.5 ppt ). A std "real" Lab grade reftract will always be off 1.5 ppt. Reason, there are two kinds of Salinity , i.e., NaCl Salinity, which these meters are set to and Seawater Salinity, which they are not set to. 35 ppt NaCl (table salt) does not equal 35 ppt Seawater but 33.5 ppt Seawater. That scale you see in that refract is a NaCl scale and not a Seawater scale. There is no company, although many claim, that make hand-held refract for seawater. Light does not bend/refract in NaCl the same way it does in Seawater and is the reason behind calibration. Once calibrated it is only good for a narrow range due to the skew effect of having the wrong scale for seawater. The PinPoint cal solution should just be put on the refract and the screw turned /calibrated so the meter reads 3.5 % or 35 ppt or 1.0264 @ 25 C = 35 ppt NSW.


After a lot of PM and talks with Randy and re-editing the final out come was this article.
Refractometers and Salinity Measurement
http://reefkeeping.com/issues/2006-12/rhf/index.php

 

[Boomer]

Made a error here

1.0235 ( 31 ppt ) and not 1.0205 (27.5 ppt ).


JohnS
Here is the link to the thread I got the info from in case you want to read more on the subject.


I just noticed that this "thread" is actually Randy's article. I did not check it before so you did good

 

[Carlo]

Good description of the refractometer Boomer. I didn't feel like trying to explain it since it really doesn't matter to much for the typical person once calibrated properly.

That's why I took the easy way out with the statement "Without getting overly complicated PSU in our environment can be thought of as the same thing as salinity." While not technically correct, close enough after calibration.

Carlo