Which would you believe?

[simplycoral]

Originally Posted by whatcaneyedo

I've compared several hydrometers with my refractometer and I've seen some that were out as much as 0.006.

I also use a sample of known salinity to calibrate my refractometer yearly http://www.jlaquatics.com/product/pp...+Solution.html so I feed confident that I'm getting accurate results.

Hi,

Definitely the way to go! I will order some now, before i go reducing the levels! Thanks..

S

[naesco]

OK I will go against the flow. I think it is another toy for the boys. But each to his own.

My son has one. I never use it because it is a little difficult to use compared to a cleaned after use hydrometer. If you don't clean it after use the refractometer will be off and if you don't clean the water test kits your tests will be off too.
I couldn't go through the picky calibration required by a refractometer and go to the trouble of buying the calibration solution before it gets stale and all that stuff.

I wonder how many reefers who own them go through the calibration stuff or simply just use it?

It is easier to simply plunge the hydrometer in the tank and scoop up the water to be tested and viola, you are bang on again. (and clean it after use)

Take a look at the this thread in advanced acquarist. It seems to confirm what I have posted.
http://www.advancedaquarist.com/2006...=refractometer

[StirCrazy]

one thing with the plastic swing arms is they are all different by a bit... they are mass produced and there are varencies. at one point I bought 3 of them and they all read differently.

also as they age they get worse. the plastic eventualy adsorbes water and changes there readings over the years.

Steve

[StirCrazy]

Originally Posted by naesco

Take a look at the this thread in advanced acquarist. It seems to confirm what I have posted.
http://www.advancedaquarist.com/2006...=refractometer

all that confirms is that swing arms are not accurate between different brands.. there is a 0.006 differance in ranges on the same solution between the different brands.. to bad he didn't buy 6 og the same type and do it.. you would have seen the same type of readings.

now having said that refractoemters can be wonkey also.. you have to buy a quality unit with temp compensation. you do get what you payfor in refractometers and personaly I would not buy one under 100 bucks.

Steve

[naesco]

Originally Posted by StirCrazy

all that confirms is that swing arms are not accurate between different brands.. there is a 0.006 differance in ranges on the same solution between the different brands.. to bad he didn't buy 6 og the same type and do it.. you would have seen the same type of readings.

now having said that refractoemters can be wonkey also.. you have to buy a quality unit with temp compensation. you do get what you payfor in refractometers and personaly I would not buy one under 100 bucks.

Steve

Here is the author's concluding opinion after testing 6 USED hydrometers.
"It is my opinion after seeing these results that plastic hydrometers are perfectly acceptable for use in the hobby. I would say they are even acceptable for use in research. Their precision appears to be well within the range of projects I’ve seen conducted in laboratories. Their accuracy is variable, but with a known (and easily found) correction factor these hydrometers perform quite well."

I bet after one year, we looked at the results of 6 refractometer readings, we would have 6 different readings as well for the reasons given in my earlier post.

But I agree that if you spend good money for a quality refractometer, carefully clean it after use, diligently follow the calibration procedures, and if you are the type that washes and dries your dishes immediately after use and put them away, a refractometer is for you.

[justinl]

yup, I fully agree with naesco. While hydrometers can be far from accurate, they are almost always very precise; That is, they are off by the same amount, in the same direction, every time. For example, on a sample of known salinity of 1.025, my hydrometer reads low at 1.018; so I just aim for 1.018 all the time. I have had my hydrometer for three years and recalibrate it every few months but it has yet to change. You also have to keep the things stored in freshwater; I keep mine in a tote that I store topoff water in.

[mark]

Reason why I gave up with the swing arm is one I'd been using for awhile (always rinsing between uses) one day was off 0.006. Didn't drop it, arm swung freely, no signs of damage, etc and it was toast. Can handle a consistent error but not jumps.

Sure a refractometer can go out of cal as well, but just seems they're more sturdier.

[Aquattro]

I used a plastic hydrometer for more than 10 years, it was dead on any time I compared it to a refractomer. Then one day, nope, it was way off. They are not reliable, and a refractomer is a more accurate instrument. Or, you could use a lab grade glass hydrometer, these are very accurate.

And paying over $100 for a $50 instrument? Hmm, a foolish Steve and his money...you know the saying I'm not even sure you can buy one for that much?

[whatcaneyedo]

For someone with a Masters Degree thats not a very good experiment. Why only one refractometer? There are many brands of different cost and quality. I've seen them range from $12 to $197 on ebay. Where is his control group? Where are the references? Where are the details period? When read with the Steven Pro article provided in the link the only idea that it seems to support is that cheep well used hobby grade equipment doesnt last.

Randy Holmes Farley PhD writes a much better article on the subject: Refractometers and Salinity Measurement http://www.reefkeeping.com/issues/20...f/index.php#12

I've owned my Refractometer (the brand J&L sells) for 3 years. After 2 years I calibrated it with a solution of known salinity for the first time and it was low by 0.001

[naesco]

I think the whole discussion of salinity and it measurement is academic. Nobody is going to go to the trouble of calibrating in the manner Farley suggests. The important things are.
1. That salinity is within an acceptable range.
2. That is doing water changes you check the salinity of your tank, the salinity of your new water, and the salinity after you do the water change.
Whether you use a hydrometer or refractometer that is off target makes no difference because the off target reading is consistent for all 3 tests.
The important thing is that there is not a sudden change of salinity.

In the same way that all reefers would question a unusual water test that reads too high or low Ca or anything else and seek another test kit, if you tested an unusual salinity it would be time to buy a new hydrometer for 15 bucks or calibrate your refractometer.

This article in advanced aquarist (look under salinity) measures the changes in salinity in one day at a reef. You can see that in nature salinity drops and falls during the day. So measuring to a precise reading is irrelavent as long as you are within the acceptable range.
http://www.advancedaquarist.com/2009/6/aafeature