Have a Refractometer myself but do laugh a bit as we (myself included) go on how they're so much better than a swing arm hydrometer.

Been ages since verified mine against ro water and never have actually made a test solution for the range in which I use mine. Really without frequent verification there are no better than a swing arm type.

With swingarm & glass hydrometers people often don't realize or forget that these are calibrated at a set temperature and if the water you are measuring is significantly off that temperature, it will affect the reading. Most of the newer refractometers have automatic temperature compensation so provided you wait a few moments for the liquid to reach temperature parity with the refracto, you're good to go.

I just measured my tank water with 4 different components:;

Glass Hydro with thermometer: 1.024+ @ 74 Fahrenheit (there's a mark at 78 F so I assume that's the manufacturer's calibration temperature)
Refractometer: 1.024+ (auto temp compensation)
Instant Ocean swing arm: 1.0234 @ ? Fahrenheit, presumably same as glass hydro
Coralife Deep Six swing arm: 1.0216 @ ? Fahrenheit - same story as IO swing arm

Note the extra decimal place for the cheapo swing arm jobbies. That's because the scale on both of these is fairly large making it easier to read off to that level of accuracy. Both the glass hydrometer and refracto scales are much tighter and for me this makes it almost impossible to read anything beyond that 3rd decimal. So one could argue that the swing arm hydros offer an advantage in this regard, provided they are accurate to begin with and one has the temperature compensation chart handy.

I kind of like the floating glass hydrometer. It's a tried and true technology. Different versions of these have been used for decades to measure specific gravity of battery acid, anti freeze in your radiator, sugar content for potential alcohol of that home made wine.... Same goes for refractos, one for almost every flavour.

At $50.00 each and as delicate a rose, this is the glass hydrometer to use if you want to measure your SG/Density to an accuracy of 0.0005

Fisherbrand* ASTM* Specific Gravity Hydrometers for Liquids Heavier than Water > ASTM: 111H; Range: 1.000 to 1.050

Hydrometer, Specific Gravity; Fisherbrand ASTM; For Liquids Heavier than Water; ASTM: 111H;Range: 1.000 to 1.050; Division: 0.0005; 330mm L; Made from polycarbonate for glass-like clarity; Use with11-582-1 Cylinder

God I love lab gear.



http://www.fishersci.com/wps/portal/...e&fromSearch=Y

I have a refractometer. I use it to calibrate my Sea Test Hydrometer. I have found that my hydrometer is out by .03! So, when I use it on a day to day basis i just add .03 to it and it's corrected. The real key is having the consistient salinity. That includes same salinity in the tank and water change salinity.

I re-test my hydrometer every time I do a water change just to make sure it holds.

Remember resolution is different than accuracy.

+1 on the consistency. I usually double/triple check to ensure my water change salinity is as close as possible to the display water.

Here are some photos of my measurements with the different 'instruments'.

IO Swing Arm 1.0234

http://hlj1yw.blu.livefilestore.com/...OSwingArmB.jpg

Coralife Swing Arm 1.0126

http://hlj1yw.blu.livefilestore.com/...eSwingArmB.jpg

Made In Taiwan Floating Glass 1.024+ (same result as refracto)

http://hlj1yw.blu.livefilestore.com/...lassHydroB.jpg

what about pinpoint salinity meters?

1.0126?, good thing you cross check with the others:biggrin:

He, he, I haven't used the swing arms for quite some time. I've been using the refracto and floating glass hydro for quite a while now. Just thought I'd bring the swing arms out and give everyone a picture... worth a thousand words I'm told.

That's how a calibrated glass hydrometer works. With a couple of known solutions measure the standard deviation and then apply that deviation to the observed reading.

So once you know your hydrometer consistently reads +.03, add that to the observed result for an accurate measurement.

Of course by measuring anything you are changing it so you can never have a "TRUE" 100% no questions asked result. :lol: