Three months ago I began a new project to test old
hydrometers. The purpose of the test was to compare several old,
very used, hydrometers with other “more accurate” devices.
Currently the marine aquarium hobby uses refractometers as the
gold standard for measuring salinity/specific gravity. Therefore
a recently calibrated refractometer was being compared side by
side with several hydrometers.
This project is temporarily on hold. Initial data is presented
below. However new information has been published since the
inception of this project. Unknown to this author a good friend
and fellow author was also studying this concept. My friend
Steven Pro recently published his results (Pro, 2006) in the
online magazine Conscientious Aquarist, and can be found here.
Steven’s tests include using brand new hydrometers straight
out of the box. My test was designed to use old and well used
hydrometers. Anyway the project will continue as Steven and I are
now discussing ways to improve the tests, and ways to combine the
Refractometers are considered by the vast majority of
aquarists to be superior (in terms of accuracy and precision) to
the common plastic hydrometers. Because refractometers are only
accurate when recently calibrated it is my hypothesis that these
refractometers are not any better, and may even be less accurate
than plastic hydrometers.
At this stage of the project I have used 1) a recently
calibrated refractometer 2) an electronic salinity measuring
device with a digital readout 3) and four used plastic
hydrometers. These devices were all used to measure 5 different
aquariums. The refractometer was recently calibrated (the purpose
of this test) and the digital instrument was brand new still in
the box. That digital did come with calibration solution. The
instrument was tested with that solution and found to be accurate
out of the box.
|Aquarium||Refractometer||Digital Display||Deep Six||Marine Environment||Instant Ocean||Aquarium Systems|
At this stage I am only presenting opinion. No statistics have
been performed and I admit that the condition of the hydrometers
is not something I could reproduce. 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. His vision
is to see this type of collaboration lead to further advancements
in aquarium husbandry. While not in the lab he is the former
president of one of the Nation’s largest hobbyist clubs, the
Wasatch Marine Aquarium Society
(www.utahreefs.com). Adam has earned a BS
in Marine Biology and an MS in the Natural Resource and Health
fields. Adam can be found at