question about a hydrometer

[sk8r_dave]

Originally Posted by xDave
Ahhh baloney! Nothing wrong with hydrometers, yours is just bad.
According to tests done by Adam Blundell, M.Sc. "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."
(Adam Blundell M.S. works in Marine Ecology, and in Pathology for the University of Utah. He is also Director of The Aquatic & Terrestrial Research Team, a group which utilizes research projects to bring together hobbyists and scientists. While not in the lab he is the former president of one of the Nation's largest hobbyist clubs, the Wasatch Marine Aquarium Society. Adam has earned a BS in Marine Biology and an MS in the Natural Resource and Health fields.)
He isn't the only one that finds cheap plastic hydrometers very accurate. Another hydrometer test

xDave, even if this is true (people had some bad experiences with them.) From a finachal stand point. Wouldn't it be a better decision to buy a refractometer insted of paying $20 every few months?

 

[xdave]

When I bought mine for $5 I tested against a refractometer and it was perfect. I've tested it every few years out of curiosity. It's been over 20 years since I bought it and it's still right on the money.
The main variable that effects the difference between salinity and specific gravity is temperature. If your tank water and the water your adding are both at the proper temp it is a mute point. Almost anywhere your get livestock will give you the S.G. requirements, not the salinity. If you measure the S.G. of the water at the temp they suggest there is no problem.

 

[xdave]

Originally Posted by LexLuethar
You cannot conduct a VALID test one time and tell my that the results are statistically accurate - because they are not. Conduct that same test for 7 - 14 days with all hydrometers and THEN you can make a case.
If your hydrometer gives varied readings on water at the same salinity and temp, it is user error. It has 1 moving part with 0 friction. How's the reading going to change?

 

[lexluethar]

Originally Posted by xDave
If your hydrometer gives varied readings on water at the same salinity and temp, it is user error. It has 1 moving part with 0 friction. How's the reading going to change?
Salt creep (multiple uses), air bubbles, a fraction of a difference in temperature, an uneven surface a degree or two off, i'm sure there are a few others.
You were correct in stating that mine is probably broken, to be that far off seems to be out of the ordinary even with people that have also had issues. To claim it was user error is a bit crass, it was a level surface and there were no air bubbles. Use what you want i don't care i was just stating what i've found in past experience.
I just find it difficult to believe his measurements were that exact, and regardless you can't conduct a study, do it once and make a valid conclusion - that is all I was saying with the last post.

 

[xdave]

Using a hydrometer with leftover salt, bubbles, or reading it when not level is user error, not equipment error. I'm sorry if that sounds crass but not following the directions is pretty much the definition of user error. Using a refractometer with salt left in it will also give inaccurate results.
How can you suggest that someone with a B.S. in marine biology, the director of the Aquatic & Terrestrial Research Team, a group which utilizes research projects to bring together hobbyists and scientists, a man who's bio contains the phrase "when not in the lab", didn't properly conduct a simple comparative test?