Refractometer - reading the scale

[mattseattle]

Ok I have another question and it's regarding a post I found on reefcentral in the chemistry section. It states this:
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So, you want it to read 36 or 1.027, as this refract like 99.99 % of them DO NOT measure seawater, no matter what they say. These units are based on a NaCl / Sodium Chloride scale. This scale is not the same as a seawater scale, it is low by 1 unit, so you want it to read one unit higher, i.e. NSW is 35 ppt so you want it to read 36 ppt. If you are using the SG scale you want it to read 1.027, NOT 1.026, which is NSW.
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so this says that if my refractometer is reading 1.026 then the salinity of my water is actually 1.025?

is this a known 'fact' about refractometers that you have to add 1 unit to the reading?

 

[esmith]

I haven't read that, but would be interested to know. I assumed that they could read salt water just the same as any solution.


Eliyah

 

[mattseattle]

yeah i am really curious as well....hopefully someone will have more information for us.

 

[NaH2O]

Matt, my understanding is the readings are off 0.001 on the specific gravity and not the salinity. So, if you read your salinity to be 35ppt you should be good. If, however, you want to go by the specific gravity, and you want it to be 1.026, then your refractometer should read 1.027 (basically the same as what you said ). It is true that they are based on NaCl solutions, but I think there is one available that is a true value ---- it is extemely expensive, though.

How often does everyone recalibrate their refractometers? Once a month or more often than that?

 

[mattseattle]

thanks Nikki for the info. I have been reading the ppt side even though the information i grabbed off reefcentral says that both sides of the scale are off. hmmmmmm

well i've only had mine for a month so i've only calibrated it that once. guess a month is a good rule of thumb.

 

[NaH2O]

Here is a good article:

Specific Gravity: Oh how complicated

 

[NaH2O]

I have been reading the ppt side even though the information i grabbed off reefcentral says that both sides of the scale are off

Matt, you may be right. I guess if you shoot for the range 34-36 ppt, you should be good, eh? I'll see if I can dig a little more for a better understanding of how the readings work. Hmmm....this hobby is so complex, even something as simple as "What is your specific gravity" gets difficult to understand

 

[mattseattle]

geeez....that article almost blew my mind.

thank you very much for search for the answer.

 

[jks1]

I didnt know this about the refractometers. Thanks

 

[mattseattle]

i guess most of us don't as it was purely accidently i came across an article talking about it.

 

[mattseattle]

any others have facts/opinions on this?

 

[wanareef]

Just great, I've been reading the thing worng. So when I read 1.023, it's actually 1.022 and now I have to raise it up a bit.

OK, So what I did to "zero" the thing was use ro/di water. Did I do this right? Or ??? There were no instructions with the refractometer when I got it and just used "common cents" err sense.:lol:

 

[mattseattle]

that is what i did as well but apparently we should add 1 unit on both sides.