Refractometer and water temp.

[normanknight]

Another question for the experts!
I keep reading that the water temperature should be the same when testing two different sources for specific gravity. It would seem to me that adding 3 drops of water to the refractometer would immediately change the water temperature to the temperature of the refractometer and would have little effect on the original temperature. Where is my thinking wrong?

 

[florida joe]

Originally Posted by normanknight
http:///forum/post/2593390
Another question for the experts!
I keep reading that the water temperature should be the same when testing two different sources for specific gravity. It would seem to me that adding 3 drops of water to the refractometer would immediately change the water temperature to the temperature of the refractometer and would have little effect on the original temperature. Where is my thinking wrong?
Your refractometer should compensate for the different temperatures of different samples. The only time you want controlled water temp is when you are calibrating it Oh and I am the last person to comment on someone’s thinking

 

[lexluethar]

I never really understood the concept of temperature and refractometers. Refrac. are supposed to measure salinity by how light bends through the water - so how would temperature effect light? I always thought that is what made refrac. so superior because temperature didn't effect it. I'm sure i'm totally wrong here, but i didn't think the temp mattered. Just callibrate the refrac. w/ ro/distilled water and you are set.

 

[normanknight]

Thanks for the input about temperature. I just kept thinking about it and it didn't make total sense to me. I can understand using the same temp water for calibrating the instrument though. Great to know I can always get some good feedback on this board.
Norman

 

[bang guy]

Originally Posted by normanknight
http:///forum/post/2593390
Another question for the experts!
I keep reading that the water temperature should be the same when testing two different sources for specific gravity. It would seem to me that adding 3 drops of water to the refractometer would immediately change the water temperature to the temperature of the refractometer and would have little effect on the original temperature. Where is my thinking wrong?
The only flaw in your thinking is that refractometers don't measure Specific Gravity.

 

[lexluethar]

But some refrac. have specific gravity numbers on it, which is kinda confusing.
So does temperature matter when using a refrac bang?

 

[florida joe]

Originally Posted by Bang Guy
http:///forum/post/2593851
The only flaw in your thinking is that refractometers don't measure Specific Gravity.
If you are scratching your head IMO what bang means is the method in which a refractometer works is really giving you salinity but most have a corresponding chart so you view both salinity and specific gravity

 

[lexluethar]

Ya i remember a while back having this conversation with Dark and a few others. So do you know why some refrac have specific gravity on them? I realize that they are two different measurements, and that IN GENERAL are their equal. LIke 34 ppt salinity is usually 1.026 specific gravity. I'm just trying to get a better grip on what are comparable SG and salinity (realizing that with any SG temp matters).

 

[bang guy]

Originally Posted by LexLuethar
http:///forum/post/2593858
But some refrac. have specific gravity numbers on it, which is kinda confusing.
So does temperature matter when using a refrac bang?
Yes, I agree it is confusing. What Florida Joe said is absolutely correct.
ATC refractometers change the temp of the water drops to room temp to get a consistent salinity reading. Salinity doesn't change significantly with temperature differences so the Salinity reading on the refractometer will match the salinity of your tank regardless of what temperature you keep your tank at. The refractometer does need to be kept at room temp though. If you set it in the sun or on top of your canopy where it's hot then the reading will be slightly off.
Ignore the Specific gravity reading on a refractometer, just read the salinity side.

 

[lexluethar]

Thank you bang!

 

[normanknight]

Thanks everybody.
This is all getting very interesting and is making sense. I think the best thing is just keeping the refractometer at room temp, then all the readings should be accurate. I am sure glad I replaced my hydrometer.

 

[dennis210]

Just a question here, but in many books I find charts with both SG and Sal.
With a refractor reading of 35 or 36 the corresponding reading on it is 1.0265. There is a chart in Tullock's work showing natural salinity of seawater in the vicinity of reefs as 35 or 1.026. Most texts recommend 1.023 or 1.024.
This in itself can be confusing. So since there is a chart for converting density (SG) to salinity can't it be inferred backwards going from a known salinity to a inferred density. That was what I thought all refracors did with their built in scales.
Just asking!
Dennis

 

[bang guy]

Originally Posted by Dennis210
http:///forum/post/2594460
Just a question here, but in many books I find charts with both SG and Sal.
With a refractor reading of 35 or 36 the corresponding reading on it is 1.0265. There is a chart in Tullock's work showing natural salinity of seawater in the vicinity of reefs as 35 or 1.026. Most texts recommend 1.023 or 1.024.
This in itself can be confusing. So since there is a chart for converting density (SG) to salinity can't it be inferred backwards going from a known salinity to a inferred density. That was what I thought all refracors did with their built in scales.
Just asking!
Dennis

Real numbers will help demonstrate I believe. But first I want to mention that it's the Salinity of the water that matters, not the density. So there's no real reason to mention density at all, 35ppt - 37ppt is the important measurement.
OK tank water is 35ppt and the temperature is 86F. This is what I maintained on my Nano tank a couple years ago. This is a Specific Gravity of 1.023. If I look at the S.G. scale on my refractometer it reads 1.0265. Well, the Salinity reading on the refractometer is spot on at 35ppt but the S.G. reading is just plain wrong. It's not even close.
But like I mentioned before, S.G. doesn't matter to reef animals, Salinity is the important parameter.

 

[lexluethar]

I also read somewhere (don't remember where) that the reason on a refrac. that they have SG was hobbiest were upset because they were so used to using SG that having salinity was confusing. A lot of people complained and so manufactureres started showing both on a refrac - when like bang explained it really had no meaning because temperature isn't taken into effect. Because a higher temperature will yield a lower specific gravity (but the what really matters is salinity).