hydrometers

[geckofrog]

It's not an assumption by the experts, refractometers measure the salinity level differently then how an hydrometer does.

Hydrometers measure the weight of the water to determine the salinity level.

Refractometers measure the angle of the light bending from the salt in the water.

I prefer refractometers, but that is just my opinion

 

[Nabber86]

<a href=showthread.php?s=&postid=8265979#post8265979 target=_blank>Originally posted</a> by Steven Pro
I am just wondering. Why does everyone assume a refractometer is any more accurate than a hydrometer? Both are manufactured products. Why must one be made to a higher standard than the other?

Cheap refractometers (<$100) are less accurate than a hydrometer. It’s just that a lot of people wrongly equate ease of reading/ease of use with accuracy. It is the same way with thermometers: most people assume a digital thermometer is more accurate than a glass thermometer because it is easier to read - to the 1/10 of a degree no less.

A refractometer also “looks” cooler than a hydrometer. Refractometers look futuristic and sexy while a hydrometer looks like something that Archimedes put in his bathtub thousands of years ago.

I have used hydrometers in a lab setting for years and IMHO, no instrument is better at measuring specific gravity than a good hydrometer. Such as this model that is available from Fisher Scientific:

https://www1.fishersci.com/Coupon?cid=1328&gid=191074

If you read the product description you will see that this particular hydrometer is calibrated according to ASTM E 126 specifications and includs a certificate to indicate traceability to standards provided by NIST. All that for less than $50. How many of these cheap Chinese-made refractometeres available on the net are factory calibrated to spec and come with traceable documentation?

 

[Nabber86]

So does anyone out there have a refractometer that came with documentation of accuracy?

Anybody?

 

[neotekz]

<a href=showthread.php?s=&postid=8269474#post8269474 target=_blank>Originally posted</a> by Nabber86
Cheap refractometers (<$100) are less accurate than a hydrometer. It’s just that a lot of people wrongly equate ease of reading/ease of use with accuracy. It is the same way with thermometers: most people assume a digital thermometer is more accurate than a glass thermometer because it is easier to read - to the 1/10 of a degree no less.

A refractometer also “looks” cooler than a hydrometer. Refractometers look futuristic and sexy while a hydrometer looks like something that Archimedes put in his bathtub thousands of years ago.

I have used hydrometers in a lab setting for years and IMHO, no instrument is better at measuring specific gravity than a good hydrometer. Such as this model that is available from Fisher Scientific:

https://www1.fishersci.com/Coupon?cid=1328&gid=191074

not everyone uses these hydrometer though. most use those cheap hydrometers that they sell for 10 dollars at the LFS and those are horribly unaccurate.

 

[antony1103]

I agree with Nabber. If you get a refractometer, plan on spending $150 or more for a good one. I have found that a good hydrometer is better than than cheaper refractometers and give more consistant results.

 

[Nabber86]

not everyone uses these hydrometer though. most use those cheap hydrometers that they sell for 10 dollars at the LFS and those are horribly unaccurate.

I am not so sure about that. Steven Pro's artical above shows that plastic swing arm hydrometers (that he tested, anyway) are remarkably accurate.

A refractometer is a "black box". Without any documentation as to it's accuracy it is Garbage in/Garbage out. I have a $50 hydrometer with "proof" that it is accurate to winthin a stated degree. I have yet to see any refractometer for less than about $2000 that comes with any documentaion of accuracy.

Just remember that any instrument is only as good as it is calibrated and documented. Based on that, a $10 undocumented plastic hydrometer is just as good as a $200 undocumented refractometer. Taking it a step further, a $50 documented hydrometer blows away a $200 undocumented refractometer.

 

[Nabber86]

<a href=showthread.php?s=&postid=8270822#post8270822 target=_blank>Originally posted</a> by antony1103
I agree with Nabber. If you get a refractometer, plan on spending $150 or more for a good one. I have found that a good hydrometer is better than than cheaper refractometers and give more consistant results.

It's more like $1000 for an "Economy" refractometer that might beat a $50 hydrometer:

https://www1.fishersci.com/Coupon?cid=1328&gid=196812&details=Y

 

[neotekz]

i thought that's why u have to calibrate a refractometer before u use it. a cheap swing arm might be just as accurate as a refractometer but the thing that turned me away from them is that they so hard to use. it would always take me 3-4 tries before i was sure that there was no bubbles on the arm even so i was still suspicious since the smallest bubbles can change the reading. i'm sure that the hydrometers aren;t as unaccurate as people tend to say but its user error that throws their reading off, the end result is the same though.

i had no idea that there was something more accurate than those refractometers avaliable to hobbist at a reasonable price.
how does that hydrometer that u posted a link to work? is it the floating ones?

 

[MyCatsDrool]

Hmmm....

I was thinking about this after reading this thread and the idea hit me that a sundial more accurately tells the position of the sun (time of day) than a digital watch.

Newer, fancier technology is not always greater than tried and true methodology.

 

[sjfishguy]

Nabber, what kind of lab uses hydrometers? Are you serious? I would go with a refractometer everytime. How does one recalibrate the TYPICAL hydrometer? Can easily recalibrate a refractometer with DW. I have lined up for swing arm hydrometers and each one reads something different by .002. Not with refractometers.

 

[hypermikie]

The thought that one must use "this" particular piece of equipment because it has documented calibration is a bit harsh.

As sjfishguy said one can easily calibrate their own refractometer at home, with a easily available and reliable known source.... Distilled Water.

One can not however easily calibrate or check the accuracy of a "typical" hydrometer at home.

 

[Nabber86]

I can see hear that there is a gross misunderstand of the science of collecting data and confusion as to what defines precision and accuracy.

I have lined up for swing arm hydrometers and each one reads something different by .002. Not with refractometers.[\QUOTE]

The fact that your refractometer reads the same thing everytime and you get a varience of 0.002 when using various hydrometers sez absolutley nothing about the accuracy of either instrument. Your refractometer could be off by more than 0.002 inwhich case the hydrometer would be more accurate. Although the refractometer, in this case, would be more precise. If your refractometer does not come with a certificate, you have no idea how accurate it is.

How many times do you see somebody post the following:

"I have used a swing arm hydro for years and it always read 0.025 and then one day my buddy checked the SG with a refractometer and is was like 1.035, yada, yada, yada. Therefore, swing-arms are crap". In this case, neither instrument is documented and all you can say is that you have a relative percent difference of 33 and that the swing arm is very precise. You cannot assess the accuracy of either instrument with the data provided.

As sjfishguy said one can easily calibrate their own refractometer at home, with a easily available and reliable known source.... Distilled Water.

One can not however easily calibrate or check the accuracy of a "typical" hydrometer at home.[\QUOTE]

I am thinking that there is a little confusion between calibration and checking against a known standard. It is just as easy to float a hydrometer in distilled water as it is to put a drop on a refractometer. It is also easy to measure out a known mass of salt, dissolve the salt in a known volume of distilled H2O, and make your own standard solutions. You should probably do a standard check on either instrament from time to time.

 

[kravi]

The hydrometers are generally very precise, and accurate to a fixed degree.

What this means, is that if you take your water to a store with a calibrated refractometer (once) and find out that your water level is 1.025, while your hydrometer reads 1.029, you can be certain that every time your hydrometer reads 1.029 it is 1.025.

It may be a little skewed, but allowing for that, you can figure out and get accurate readings from it. It is also significantly cheaper.

--Me

 

[sjfishguy]

Nabber: "The fact that your refractometer reads the same thing everytime and you get a varience of 0.002 when using various hydrometers sez absolutley nothing about the accuracy of either instrument."

Your right, its says nothing about accuracy, but it does say something about percision.

Accuracy- the degree of conformity with a standard (the true measurement)

Precision- the ability of an instument to replicate a value (whether the value is a "accurate" or not)

I am still not sure what you are talkin about as far as "documented" goes. Who cares? As long as your instument is accurate and precise when testing a KNOWN standard (i.e. distilled water, titrated solution, etc.), why do I need a piece of paper? I just tested it myself. With a typical hydrometer you can not do either of these. The arm does not go down to 0 so you cant test it with DW and you cant move the arm to calibrate if you find out it is indeed imprecise. How can 10 people stand in a room, calibrate their $50 refractometers, test the same water out of the same tank, and all get the same reading of 1.025? It has been done at my local reef club. Now take the same 10 people with 10 random hydrometers (remember, they cant be brand new, just like the refractometers werent brand new (I dont even think this would matter, but just to be consistent) repeat the same test. I would put money on less than 5 of them having the same reading, and I bet you would too.

You also state you can calibrate a typical hydrometer at home. How do you calibrate the marineland or IO hydrometer?

And from my experience, I held out on getting a refractometer too. Finally got one. My IO hydrometer said my tank was 1.025. My friend's IO hydrometer said it was 1.023. The refractometer said it was 1.030! Then I had someone else check it with their refractometer- 1.30. And remember, the refractometers were calibrated, now you tell me??????..............

 

[neotekz]

<a href=showthread.php?s=&postid=8276074#post8276074 target=_blank>Originally posted</a> by Nabber86

I am thinking that there is a little confusion between calibration and checking against a known standard. It is just as easy to float a hydrometer in distilled water as it is to put a drop on a refractometer. It is also easy to measure out a known mass of salt, dissolve the salt in a known volume of distilled H2O, and make your own standard solutions. You should probably do a standard check on either instrament from time to time.

so are u saying that rodi is NOT a known standard? even if my refractometer is not accurate i rather it be percise. but i;m still not convince that a calibrated refractometer can be as unaccurate as u say.

 

[kryppy]

All you guys talking down on the hydrometers have to realise that temperatures affects them greatly. It is nice to know if it is calibrated for 75 , 77 or 80. You can't really read it correctly
without understanding this.

 

[Agu]

Ever tried to test the water in a bag of coral/fish/inverts from the LFS with a hydrometer ? Good luck . The ability to test a tiny amount of saltwater in and of itself for acclimation purposes is enough to justify the purchase of a refractometer.

BTW, the floating glass hydrometers are also subject to error unless you turn off all water flow, have no bubbles attach to the glass, and have 20/20 eyesight. Then you might be able to guess what it actually reads.

I won't even comment on swing arm hydrometers or I might have to ban myself :lol: .

 

[coolfishy101]

The floating glass hydrometers are in a cylinder, you fill the cylinder, then drob in the floating piece, there is no water flow and if there is a few bubbles, gently shake them off. sounds easier than using a refractometer. I have 4 IO swing arm hydrometers which are all accurate within .0005 of each other.

 

[Agu]

The floating glass hydrometers are in a cylinder, you fill the cylinder, then drob in the floating piece, there is no water flow and if there is a few bubbles, gently shake them off. sounds easier than using a refractometer.

Sounds like you've never used a refractometer.......... :lol:

I've screwed around with using a cylinder (bud vase actually) to float a glass hydrometer. What a pain in the behind................ and even the tiniest residual salt throws off the reading.


jme,

 

[ambaratur]

<a href=showthread.php?s=&postid=8279089#post8279089 target=_blank>Originally posted</a> by Agu
Ever tried to test the water in a bag of coral/fish/inverts from the LFS with a hydrometer ? Good luck . The ability to test a tiny amount of saltwater in and of itself for acclimation purposes is enough to justify the purchase of a refractometer.

BTW, the floating glass hydrometers are also subject to error unless you turn off all water flow, have no bubbles attach to the glass, and have 20/20 eyesight. Then you might be able to guess what it actually reads.

I won't even comment on swing arm hydrometers or I might have to ban myself :lol: .

I agree with this statement - but the eyesight is not a valid arguement as I have a refractometer and must look very carefully to read it and having glasses doesn't make it any easier. The increments are very small and it has taken practice to see it right.

Luckily for me 1.025 has a longer line than above it and below it so it helps me identify it easily.