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View Full Version : refractometers vs. hydrometers?


skeeter-doc
10/30/2006, 12:21 PM
are even the cheap refacts better/more precise than a hydrometer?

easye123
10/30/2006, 12:24 PM
yes

100 percent

IMO

the 40 dollars refractometers are awesome IMO i got mine from drfostersmith

Paintbug
10/30/2006, 12:25 PM
they are usually more accurate, not so much precise. hydrometers when kept clean, will get you consistant readings. but those readings may be off. if you can go to a LFS and have your hydrometer compared to a refractometer, they work fine. you just have to keep them very clean, and make sure no air bubbles are on the swing arm. but using a refractometer is so much easier.

skeeter-doc
10/30/2006, 12:30 PM
ok thanks, anyone else?

trippyl
10/30/2006, 12:34 PM
refractometers.

conefree
10/30/2006, 12:37 PM
Refractometer. For $40, it's a great deal. Consistent, accurate readings and easy to calibrate.

Randall_James
10/30/2006, 01:00 PM
A good hydrometer (not a swingarm type but a real floating lab type) is more accurate than 95% of the refractometers out there. A $40 refractometer is just that a $40 measuring device. A $20 - $40 hydrometer is more accurate but requires temp correction.

For aquarium use however, a $40 device is fine, for lab work it does not even come close to adequate except for comparisons readings

trippyl
10/30/2006, 01:08 PM
right, but no one is using a lab grade hydrometer for their water changes. If you are talking about hobbyist quality hydrometers vs hobbyist quality refractometers, there is no comparison.

There are many things done in research laboratories that are simply not accessible or too expensive for the average aquarist, so why we would bring them up is beyond me. Some poor shlub is gonna take your advice and buy one of these:

http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=7360&Ntt=hydrometer&Ntk=All&Ntx=mode+matchallpartial&Np=1&pc=1&N=2004&Nty=1

I question how accurate one of these things are. If they don't stick the piece of paper in just right...

OTOH, my refractometer can be calibrated and is accurate as a result.

Randall_James
10/30/2006, 02:18 PM
actually you can go down and buy a lab grade hydrometer for less than a refractometer...

And if you want accurate, the "poor shlub" is going to have a more accurate device... I added that it was not really necessary for the hobbiest... (not sure what got under your skin about this anyway)

However they need corrective readings due to thermal issues.

If you want to nit pick the question was whether hydrometers are more accurate than refractometers and typically they are..

Just not as practical for a hobbiest, but you might be surprised just how many "Schlubs" in fact use lab grade hydrometers...(after all if available, they are cheaper and easier to come by than refractometers for most local purchases)

RichConley
10/30/2006, 02:24 PM
At any given price, a hydrometer is much more accurate than a refractometer.

Those swing arm jokes really aren't hydrometers.

Refractometers are just easier to use.

cristhiam
10/30/2006, 03:40 PM
Where do you get the lab grade hydrometers?

Amphiprion
10/30/2006, 03:55 PM
<a href=showthread.php?s=&postid=8444723#post8444723 target=_blank>Originally posted</a> by RichConley
At any given price, a hydrometer is much more accurate than a refractometer.

Those swing arm jokes really aren't hydrometers.

Refractometers are just easier to use.

I have never noticed this in any of our lab equipment. Our refractometers are always more accurate AND precise, albeit not by much. Precision can be increased in any particular hobby equipment if calibrated properly. I used lab grade scales and graduated cylinders (more precise than necessary) to obtain a known standard solution of full strength seawater at 35 ppt (or PSU, whichever you prefer). I prepared large sealed batches of this solution and the only instrument, though well cleaned, etc. to give changes in accuracy (not necessarily precision) was the hydrometer. The refractometer had superior accuracy and precision from what I saw. However, I will admit that some error may have been because I found the hydrometer a bit more difficult to properly obtain a reading at the meniscus on occasions because my vision sucks. It could very well have been a bit closer or the same. If well calibrated, both pieces of equipment can be very sensitive and accurate.

Randall_James
10/30/2006, 04:00 PM
http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=7360&Ntt=hydrometer&Ntk=All&Ntx=mode+matchallpartial&Np=1&pc=1&N=2004&Nty=1

Or you can visit any lab supply and get a unit that measures from 1.000 to 1.0300

A lot of fish stores carry glass hydrometers as well.

Note that they come in a long plastic tube, this tube servers as the hydrometer jar (fill with water to be measured). Price should be in the $12 - $19 range

If you do not mind the extra cost, a refractometer is less hassle and accurate enough provided you calibrate before use (RO/DI seems to work ok for this)

Randall_James
10/30/2006, 04:07 PM
<a href=showthread.php?s=&postid=8445383#post8445383 target=_blank>Originally posted</a> by Amphiprion
I have never noticed this in any of our lab equipment. Our refractometers are always more accurate AND precise, albeit not by much. Precision can be increased in any particular hobby equipment if calibrated properly. I used lab grade scales and graduated cylinders (more precise than necessary) to obtain a known standard solution of full strength seawater at 35 ppt (or PSU, whichever you prefer). I prepared large sealed batches of this solution and the only instrument, though well cleaned, etc. to give changes in accuracy (not necessarily precision) was the hydrometer. The refractometer had superior accuracy and precision from what I saw. However, I will admit that some error may have been because I found the hydrometer a bit more difficult to properly obtain a reading at the meniscus on occasions because my vision sucks. It could very well have been a bit closer or the same. If well calibrated, both pieces of equipment can be very sensitive and accurate. Your lab has $40 refractometers? My el cheapo does not have anywhere near the resolution of my hydrometer or my good refractometer.

Nabber86
10/30/2006, 04:44 PM
I am no schlub, but I use one of these to measure SG:

https://www1.fishersci.com/Coupon?cid=1328&gid=191033

And I can PROVE that this lowly $40 hydrometer has better precision and accuracy than any refractometer used by any hobbiest on this board.

Amphiprion
10/30/2006, 05:10 PM
<a href=showthread.php?s=&postid=8445445#post8445445 target=_blank>Originally posted</a> by Randall_James
Your lab has $40 refractometers? My el cheapo does not have anywhere near the resolution of my hydrometer or my good refractometer.

No, but I tested it against one, which seemed to be precise and accurate within reason (as you indicate, this had less resolution). Absolute precision (<+/- 1ppt) is unecessary in the vast majority of cases unless you are obsessive or are doing lab work (both of which apply to myself, admittedly :( ). For our purposes and the purposes of keeping aquaria, well calibrated $40 refractometers may as well be the same as $500 lab grade ones, since the differences mean very little.

Randall_James
10/30/2006, 05:33 PM
<a href=showthread.php?s=&postid=8445845#post8445845 target=_blank>Originally posted</a> by Amphiprion
No, but I tested it against one, which seemed to be precise and accurate within reason (as you indicate, this had less resolution). Absolute precision (<+/- 1ppt) is unecessary in the vast majority of cases unless you are obsessive or are doing lab work (both of which apply to myself, admittedly :( ). For our purposes and the purposes of keeping aquaria, well calibrated $40 refractometers may as well be the same as $500 lab grade ones, since the differences mean very little. I guess you leave me awash here, all I stated in the first post is that hydrometers are more accurate than a $40 refractometer, and that also it did not matter so much as it was good enough for hobbyist use. The resolution on all these low buck refractometers is 1ppt. (fine for a hobbyist) Lab hydrometers are typically 2 to 5 times more sensitive (higher resolution) although it makes little difference in our tanks.

I still stand by my original post, hydrometers are more accurate than the $40 refractometer, however it is fine for the hobbiest to use a cheap refractometer... what is the big deal here? It really is not rocket science to see that a glass style lab hydrometer is more accurate than a $40 refractometer....

seems like a dumb battle here but oh well :)

Nabber86
10/30/2006, 08:45 PM
The bottom line is that you can purchase a quality lab grade hydrometer for $40 that comes with the following:

1) Permanently marked with individual serial numbers

2) Calibrated according to ASTM E 126 specifications

3) Certificate of Accuracy and Compliance provided to indicate calibration against standards provided by NIST

4) Accuracy meets or exceeds ASTM E 100 specifications

If you have purchased a $40 refractometer (that comes with none of the above) you cannot make any judgement whatsover as to the accurcy and precision of the instrument. Also, calibration is not somethiing that you can do at home to any appreciable degree by placing a drop of homemade di/ro water in your refractometer, zeroing it, and calling it "calibrated".

Randall_James
10/30/2006, 09:52 PM
<a href=showthread.php?s=&postid=8447376#post8447376 target=_blank>Originally posted</a> by Nabber86
The bottom line is that you can purchase a quality lab grade hydrometer for $40 that comes with the following:

1) Permanently marked with individual serial numbers

2) Calibrated according to ASTM E 126 specifications

3) Certificate of Accuracy and Compliance provided to indicate calibration against standards provided by NIST

4) Accuracy meets or exceeds ASTM E 100 specifications

If you have purchased a $40 refractometer (that comes with none of the above) you cannot make any judgement whatsover as to the accurcy and precision of the instrument. Also, calibration is not somethiing that you can do at home to any appreciable degree by placing a drop of homemade di/ro water in your refractometer, zeroing it, and calling it "calibrated". I knew a home brewer would get in on this :)

anyway you are correct zeroing is not calibrating but for aquarium use it is good enough I think. I mean we have such a wide tolerance of readings we are allowed 1.024 to 1.027 is pretty common and pretty wide spread. When brewing, the story is a lot different I guess, I had a freind that did that and it is really important that your readings are spot on.... so whens the next batch due? :)

Agu
10/30/2006, 09:54 PM
So if you have a cup of water or maybe two cups in the bag with a coral or fish , which tool will allow you to compare specific gravity for acclimation purposes ?

Accuracy is important but in my experience being able to compare two samples of water is more important. My experience is that a refractometer is more aquarist friendly.

Randall_James
10/30/2006, 10:02 PM
That is where I like the refractometers, comparisons... I do this on water changes where the actual reading is pretty insignificant but matching the existing water is. For that matter a swingarm type is even more than acceptable, for making 2 batches of water consistent with each other, easier is better :)

What I like my hydrometer for is occasional checks of the "real readings" so I can adjust if they get to far out of whack..

sjm817
10/30/2006, 10:23 PM
Dont assume the refactometer you buy is accurate, properly calibrated, or that you can calibrate it with RO/DI water.

Mine was off by .004. That may not sound like a lot, but it is the difference between 1.026 and 1.030

Thread here (http://reefcentral.com/forums/showthread.php?s=&threadid=953605) for details and how to properly calibrate it with Pinpoint solution.

skeeter-doc
10/31/2006, 10:56 AM
wow, thanks for the heds up sjm817

Amphiprion
10/31/2006, 11:15 AM
<a href=showthread.php?s=&postid=8446021#post8446021 target=_blank>Originally posted</a> by Randall_James

seems like a dumb battle here but oh well :)

If you say so :D

lllosingit
10/31/2006, 11:48 AM
Man!!!, I hate people who throw stuff like this at me, Now I have to go and buy The pinpoint solution :rolleyes:

I'm joking of course.
Thanks sjm817:D <a href=showthread.php?s=&postid=8448171#post8448171 target=_blank>Originally posted</a> by sjm817
Dont assume the refactometer you buy is accurate, properly calibrated, or that you can calibrate it with RO/DI water.

Mine was off by .004. That may not sound like a lot, but it is the difference between 1.026 and 1.030

Thread here (http://reefcentral.com/forums/showthread.php?s=&threadid=953605) for details and how to properly calibrate it with Pinpoint solution.

Randall_James
10/31/2006, 11:51 AM
<a href=showthread.php?s=&postid=8450957#post8450957 target=_blank>Originally posted</a> by lllosingit
Man!!!, I hate people who throw stuff like this at me, Now I have to go and buy The pinpoint solution :rolleyes:

I'm joking of course.
Thanks sjm817:D Lets not even start on electronic meters.... :lol:

sjm817
10/31/2006, 05:48 PM
The Pinpoint cal fluid is $3.50. Not a bad investment to properly calibrate your refractometer.

Steven Pro
10/31/2006, 06:03 PM
I found those cheap, plastic, box-style hydrometers from Marineland Labs/Aquarium Systems to be surprisingly consistent.

http://www.wetwebmedia.com/ca/volume_3/cav3i4/hydrometers/Impressions.htm

Nabber86
10/31/2006, 08:22 PM
<a href=showthread.php?s=&postid=8447920#post8447920 target=_blank>Originally posted</a> by Randall_James
I knew a home brewer would get in on this :)
.... so whens the next batch due? :)

You should see my collection of "proof" hydrometers.....:beer:

Randall_James
10/31/2006, 10:11 PM
<a href=showthread.php?s=&postid=8453394#post8453394 target=_blank>Originally posted</a> by Steven Pro
I found those cheap, plastic, box-style hydrometers from Marineland Labs/Aquarium Systems to be surprisingly consistent.

http://www.wetwebmedia.com/ca/volume_3/cav3i4/hydrometers/Impressions.htm I checked my 2 against my lab unit and they were both within .0008. I did find that without regular vinegar washes they started to drift a bit. It is surprising to see all of those read the same however, bully for mass production :) Biggest headache I have with them is the little micro bubbles that form on the arm itself (good whack with a pencil eraser fixes that)

Steven Pro
11/01/2006, 05:47 AM
<a href=showthread.php?s=&postid=8454989#post8454989 target=_blank>Originally posted</a> by Randall_James
Biggest headache I have with them is the little micro bubbles that form on the arm itself Tell me about it. It took 3-4 attempts per hydrometer to get them to fill without bubbles.

3 or 4 attempts per hydrometer times 12 hydrometers equals a very frustrated fish geek

skeeter-doc
11/02/2006, 01:37 PM
um, when I get bubbles on my swingarm, I just use a chopstick to get them off the arm, and it seems to work for me