Which would you believe?

[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