Hydrometer vs. Refractometer Test

[ABlundell]

Hello everyone,
So I am in the middle of writing an article on Hydrometers vs. Refractometers. It follows along the lines of my friend Steven Pro's article. Before I publish this I would like to hear any stories you have had (good and bad) about using either hydrometers or refractometers.
Feel free to post on the current discussion http://blogs.frags.org/showblog.php?bid=303
or post below on this topic.
Thanks so much,
Adam

 

[Chihuahua6]

I have a floating hydrometer and just got a new swing arm Instant Ocean hydrometer. The floating hydrometer was reading 1.026 and the new one reads 1.031! I imagine the swing arm hydrometer would be the accurate one but how can I be sure? Just for the record there were no bubbles sticking to the arm. I have a refractometer and two other swing arm hydrometers but I haven't found them since we moved. They're packed away somewhere. When I find them I will test with them all.

 

[JDrex]

Hydrometers bug me because evaporated salt tends to stick to the measurer so after the first use you either rally have to clean it out or just understand that the reading may be off

 

[billsreef]

Hi Adam :wavehand:

The cheap plastic swing arm hydrometers and the common hobbyist glass tube hydrometers are typically inaccurate. They often read different values in the same water on the same day when doing comparisons, even checking ones from the same manufacturer against each other :eek1: Haven't used the cheap refractometers, but the lab quality one I use at home and the one I use at the lab are very stable and reliable in thier readings...and even agree with each other

 

[bubblethumper]

The dispairity between my hydrometer and a refractometer was so large (about .005) that I refuse to use a hydrometer.

I currently use a Pinpoint kit and it is EXACTLY the same as a refractometer reading

 

[Steven Pro]

The 12 new hydrometers I tested were both consistent and accurate. Although, I don't know yet how well they will hold up to extended use or how the method of cleaning will affect their accuracy and precision.

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

 

[Travis L. Stevens]

Steven, I've read that article a few times. Good one, I might add. But I'm wondering how you could have such good results so consistantly while many more people have problems. I'm not saying that your research is inaccurate or that other people are lying or not using a hydrometer properly, but it seems so amazing. Is there a slight chance that the company(s) that make the ones you tested have went through either a quality control step or have improved the way they make them? While hypothetical, it could account for your amazing luck. You may have gotten a new batch while everyone else is still using older batches. I wish that I had recorded my first Hydrometer experience better. I had the same issue of it reading far too high and it had just came out of the package. I was sitting at 1.032 when I knew it tested 1.025 at the store. I checked it using their own refractometer. I then went and bought one for myself that afternoon and rechecked my water at home and was still reading 1.025.

 

[Steven Pro]

I can't imagine that I got all 12 units from one batch. I bought them over the course of several months with the help of friends all over the country.

Since the first part was published, I have received a lot of interesting comments. Enough that I am now going to do a third part in this series. I was originally just going to do part one (linked above) and then use them all everyday for a month, one third getting a DI water rinse after use, one third getting a tapwater rinse, and a third with no rinse at all. Then, retest them all for accuracy and consistency and report the results.

Now, that will be part three. Part two will test these hydrometers against plain DI water to see how accurately they read zero, test hyposaline water, and a blind test where I don't know the salinity.

 

[six.line]

Hi Adam. Nice blog.

 

[imtopora]

My experience w/ a hydrometer is that they are very inaccurate and inconsistant. I brought my water to a fellow reefer and was tested w/ a refractometer. It tested 1.032 on the refractometer and 1.026 on the hydrometer (and I wondered why my acros were light in color).I will never again own a hydrometer.HTH

 

[Daemonfly]

Have a floating hydrometer. It's not too bad, but not a precise measurement.

Had a coralife swing-arm hydrometer, and it would give a different reading for the exact same water. Get one reading, dump water out, put more water in, get a different reading. Always have to make sure there's no bubbles stuck on the arm, etc... It always read high.

Got a refractometer and have used that ever since.

Would be nice to see a large-scale experiment though.

 

[Pico Keeper]

I use a digital salinity and SG guage, and its always dead accurate as tested against a lab grade refractometer that I also Occasionally use, mostly to know if I need to recalibrate the digital guage.

But the digi cguage is great. As for hydrometers, hardly accurate, and only occassionally consistent. If you keep them clean (flush with ro/di after use, occasional vinegar baths) and you use them properly, they can be made consistent. In which case you have to calibrate it using a refrac, so you know how far off it is, and then just adjust.

 

[Ooulophilia]

I worked at an LFS and we would always calibrate the swing arm hydrometers with the store refractometer afer a customer bought one- you would not believe the range of results we got from the same brand out of the same box. If calibrated correctly they can work but after I lost count of how many I stepped it was time for the refractometer

 

[wds21921]

I've always used the swing arm hydrometers and before that the floating glass (it was all we had back then). I've always managed to get consistent results from the swing arm type. As far as cleaning them a simple rinse is all thats necessary.
The problem with the floating glass hydrometers are they're very general in the range you can use.

I'm not suggesting they're better or equal to a refractor but I've not seen where they're so innacurate they can't be used.

 

[Agu]

I've used all three for extended periods of time.

Floating glass hydrometers are consistant, if you can actually read them in water that has no motion. I found it inconsistant when transferring water to a bud vase so the water wasn't moving, it was even worse in an actual reef tank.

Plastic hydrometers are dependent on the time of day, moon cycles, and if you're listening to certain kinds of music while brushing your teeth . Besides, many plastic hydrometers don't have a 0.00 reading so there's no way to calibrate them.

Refractometers are easily calibrated, easily used, and can be used with small amounts of water (Like when you're acclimating and don't have a spare quart of water for a glass or plastic hydrometer). The ease of acclimation comparison makes a refractometer a slam dunk imo.

 

[jstraka1]

I think one point that a lot of people overlook is the fact that a swing arm hydrometer must be placed on a level surface to get an accurate reading. I am not sure whether or not mine is calibrated properly, and I have no scientific evidence to prove it, but I can attest to the fact that if it is kept clean and placed on a stable, level surface, it can be a consistent measuring device.

 

[flyyyguy]

I use a hydrometer with confidence when im doing large projects like cooking rock or setting tanks up, but not without calibrating it to a refractometer on a regular basis. It typically reads about 5 points off, but as long as i know it........

 

[Serioussnaps]

.005 off every time on hydrometers....if you want to do it right dont use one

 

[Billybeau1]

I read Steven's article too. I bought one of those units and it was bad off the shelf. He must have gotten real lucky.

A high quality lab grade hydrometer is almost always accurate when used at the temperature it is rated for. The cheap floaters are well... cheap.

I have also for some refractometers calibrate differantly depending on whether it is one of the cheap blue ones or the more expernsive model.

There are too many factors for the swing arms to be consistently accurate IMO.

 

[flyyyguy]

<a href=showthread.php?s=&postid=8186832#post8186832 target=_blank>Originally posted</a> by Serioussnaps
.005 off every time on hydrometers....if you want to do it right dont use one

EVERY time????

Every, never, always, ARe words you should always remember never to use. Ill bet my 500 gallons of reef against your 55 i could prove you wrong on that in 10 seconds.

Regardless, they arent to be relied upon and i dont use them for my displays.