Caution for anyone using a refractometer

[fkshiu]

Originally Posted by Lance

fkshiu: After reading this thread I compared readings of my refractometer to an old hydrometer I had laying around. Refractometer read 1.026, hydrometer read 1.023. Then I tested the QT tank: refractometer: 1.025, hydrometer: 1.022. Borrowed another hydrometer from a friend: same readings.
So i am going to order some of that solution ASAP!
My corals, inverts and I thank-you my friend. Lance

Don't thank me - thank the all knowing, all seeing Randy Holmes-Farley!

[Doo]

So after reading this I decided to get some

PINPOINT™ Salinity Calibration Fluid
53.0 mS standardized fluid for calibrating the PINPOINT Salinity Monitor™ with conversion chart

The only catch is I got it from ebay and it did not come with a conversion chart

did I even get the right stuff?

What do I do now - or how do I even use it?

Any help would be great!

[Doo]

I think I found what I am looking for, but any feedback is appreciated


http://www.americanmarineusa.com/sal...onversion.html

[fencer]

Don't forget that density is dependent on temperature of your sample. Unless you have a correction factor your salt mix will be off.

[Doo]

ok - so how do I fix that?

My temp is at 79.0

[fencer]

I think you are okay. Most instruments are have a tolerance range. So you can be off on Temperature. Just as long as you do not mix salt at below 15 and I would say not much above 20C. Just be consistent when you make a batch of saltwater up.

[Reefer Rob]

Originally Posted by fencer

Don't forget that density is dependent on temperature of your sample. Unless you have a correction factor your salt mix will be off.

The 2 or so drops that you put on your refractometer will go to room temperature pretty quick Has anyone noticed a change in reading as the sample cools on the refractometer? I think the specific gravity may change with temperature, but not the refractive index.

[Canadian]

There's quite a large difference in the reading if you don't bring your sample up to (or down to) 25C - the temperature at which your calibration solution should be in order to get a reading of 35ppt. So bring the temperature of the solution up to 25C by placing the bottle in some hot water and then letting it come down while resting at room temperature.

[Reefer Rob]

Originally Posted by Canadian

There's quite a large difference in the reading if you don't bring your sample up to (or down to) 25C - the temperature at which your calibration solution should be in order to get a reading of 35ppt. So bring the temperature of the solution up to 25C by placing the bottle in some hot water and then letting it come down while resting at room temperature.

Do you warm your refractometer to 25C?

[fencer]

I know some refractometer have temp comp built in. There is a bimetaliic strip that move the vernier scale slightly with tempearture. Having said that look at the manufacturer specs.....