Why Refractometer?

[Atari]

I have always questioned this. Bassically what is the calibration solution made of? Is the sealed top air tight? How old is the bottle after it is shipped to start with? There is never much instruction with these solutions, but my bottle still seems fine after 15-16 months so I don't worry too much. I still would like to find out though.

TDS calibration solution is not mad up of water. i think it is NaCl

[psykobowler]

^^^ Still missing the point I think.

 

Anyways, that's why I use my digital meter instead of refract. Cleaning it can't be faster, even the dunk, view and rinse as been described is slower than how fast my digital works. </bragging>

 

I should vote hydro just to p1ss more people off, lol!

 

I think this tread is opening up a lot of cans of worms!!! Getting off topic from hydro vs refrac.

[HecticDialectics]

You can experiment with this if you want to see how off it can be. Try RO/DI water first. Then the calibration solution at 77°.

 

 

God forbid anyone ask how to accurately measure the temperature of their calibration solution...

 

TDS calibration solution is not mad up of water. i think it is NaCl

 

 

lol

[Sac_State]

TDS calibration solution is not mad up of water. i think it is NaCl

 

umm, and i hate to even bring this up, but NaCl is just sodium...as in the salt in the saltwater (or in this case saline solution).

[Atari]

 

 

 

 

I guess I need to go back to high school.

[psykobowler]

 

 

 

 

I guess I need to go back to high school.

 

It's ok, we are testing saltwater.

[Atari]

http://www.premiumaquatics.com/aquatic-sup...REFRACT-HD.html this one is a good one, you get a bottle of calibration fluid with it very nice and half the price of your LFS model

 

this would be my recommendation.

 

swing arms tend to get salt build up over time if not cared for properly and sometimes little bubbles settle on the arm giving you a false reading, why use something that is inaccurate or has a huge possibility to be.

 

when you can have something that will prove faithful and useful for years to come.

I order this one and it came in yesterday. It’s nice having a real number instead of an arbitrary line scratched into my swing arm.

The scratch was way off by the way so now I’m in the presses of bringing down my salinity.

[Sac_State]

just make sure to calibrate the refractometer every so often to make sure that the measurements are true. good luck, and i'm sure you'll enjoy your new "toy".

[Galloping Goose]

why refractometer...simple, its ACCURATE! Hydrometers are not.

[Atari]

I don't have a refractometer but I would image calibrating it with RO/DI water would be like calibrating your speedometer while in park. My hydrometer reads 0 when I fill it up with RO/DI water does that mean it’s properly calibrated?

funny thing is the new Refractometer came with "Supper Pure Water" as its calibrating solution... looks like i was wrong about this.

[Scott Riemer]

funny thing is the new Refractometer came with "Supper Pure Water" as its calibrating solution... looks like i was wrong about this.

I don't think you were wrong. IMO, it's better to calibrate with 53mS calibration solution.

[Atari]

I still think so too.

[Phixion]

unless that digital salinity meter is one of the higher lab grade types, such as a Pin Point or American Marine unit, then I wouldn't trust that either...and if you're talking about one of those JBJ handheld units, forget about it, that thing is about as reliable as a swing arm. digital units need to be calibrated just as often, if more more, than refractometers. The great thing refractometers is the very fact that they are not electronic, and are therefore not subject to electronic error and miscalculation.

 

Yes it should be calibrated often, but I always chack it against my refracto at the supplied 30ppt solution and it's VERY accurate, even moreso than my refracto in fact. I've come to learn that lab grade isn't always required for accuracy, it terms of like American Marine, it's an excuse to milk more money out of people. For example, the standard and lab grade pH probes have the SAME error factor precentage, the lab one just will hold proper calibration longer and is more durable, it's NOT more accurate from an error standpoint though.

 

Stevie, salinity calbration fluid is NaCl.

[Jenna]

What about the floating hydrometers? The ones that look like overgrown thermometers? How accurate are they?

[Sac_State]

What about the floating hydrometers? The ones that look like overgrown thermometers? How accurate are they?

 

about as accurate as a salinity taste test

[Phixion]

about as accurate as a salinity taste test

 

People that can actually do that are crazy! Salt water is saltwater to me, I can't tell you if it's more or less!

[NanoReefNovice]

What about the floating hydrometers? The ones that look like overgrown thermometers? How accurate are they?

Actually... A good quality float hydrometer is the most percise. Refracs are just easier.

[neanderthalman]

The problem with the floating hydrometers is that the accuracy is really poor on anything bought for the purpose. Cheaply made, cheaply sold.

 

For all arguing in this thread, here's a primer so you can actually communicate accuracy and precision properly regarding your instruments. You're driving me nuts.

 

 

Other items or terms of note.

 

Precision: Repeatability of measurements - property inherent to a device. Not subject to calibration

 

Accuracy: A measure of "closeness" to the expected or true value. Can be corrected via calibration.

 

Drift: The rate at which the accuracy of a device declines after calibration.

 

Linearity: How well a calibration at one measurement provides accuracy at another measurement. Does not change significantly over time.

 

Error: Difference between measurement and known standard. Used only when calibrating.

 

 

Ok, let's clear this up.

 

Swing-arm hydrometers are lowest in both accuracy and precision. There are a lot of factors, like bubbles, crud, level surface, conditioning (initial soak), that all work against both accuracy and precision. The fat needle does not help either. Drift can be quite high, for example, if left dry for a long time.

 

Glass hydrometers are better for precision, but not much more accurate, and could even be less accurate than a swing arm. The paper slip inside could be sitting literally anywhere. However, the advantage here is that it's a sealed unit with a constant density. So long as you keep the surface clean, and the paper inside is firmly fastened, then there will be nearly zero drift. That means that you can calibrate it once, and never have to calibrate it again. They are difficult to use, and difficult to read, as you either have to fill a tall vessel, or turn off all your pumps, and then try to read through the meniscus (curved water at glass-water interface). Calibration of a glass hydrometer would require a calibrated refractometer to measure the water, then measure the same water with the hydrometer. Accuracy of one order of magnitude is lost when you do this, so you'd better hope that the solution is accurate to at least 35.0 PPT.

 

Put simply, refractometers are superior for both accuracy and precision. The gradations are quite fine in a good refractometer, and repeatability is excellent, so you're looking at a precision of about 0.5 PPT or .0005 SG, depending on the scale you use. Accuracy out of the box can be pretty bad, but the calibration is quite simple, so this is not an issue. However, there is a lot of misinformation regarding how you have to calibrate your refractometer.

 

Someone made laughing reference to calibrating a speedometer against 0. Nothing wrong with that. In fact, in most cars it's better than calibrating against the top end of the scale. Think about it. In refractometer terms - that's equivalent to saying that calibrating at 0 is no better than calibrating at 75 PPT. Neither situation is as good as calibrating at 35PPT or 60MPH, of course, but it's not without value.

 

This is where linearity comes into play. Linearity on most refractometers is quite good. Mine personally is less than 1%. What does this mean? Here's how you can determine, roughly, the linearity of your refractometer. You should get a pack of 35PPT (53mS) solution with your refractometer. Calibrate it to 35PPT, then measure RO/DI. If you read zero, then your linearity is spot on like mine. (1% means an error of about 0.35 over this span). It will never change.

 

At this point, you know that if you calibrate to RO/DI, then your measurement of 35PPT will be within about 0.35PPT. That's plenty accurate. Save your money, even if it is only a couple bucks.