In this article, I would like to talk about the reliability of common swing-arm hydrometers. Every reef aquarist has one or has used one at one time or another. But do they really work? Just how are they manufactured? Are they tested to ensure accuracy prior to shipping them out to the every day hobbyist?
I am the absolute last person to sit around writing articles only to hammer manufacturers of aquarium equipment. However, it really blows my mind that so many reef aquarists rely on these seemingly reliable, inexpensive pieces of equipment, when literally hundreds (if not thousands) of dollars and precious marine life are at risk if they should fail.
So anyway, my curiosity got the best of me and I decided to purchase three of the most popular hydrometers to see how they measured up. The results were far from pleasing.
The three hydrometers in question are:
- Hydrometer - by Marine Enterprises, Inc.
- Deep Six - by Coralife
- SeaTesT Full Range Specific Gravity Meter - by Aquarium Systems
The first hydrometer by Marine Enterprises tested a sample of seawater at 1.023. Perfect to many hobbiests, a little low to others
The second hydrometer by Coralife measured the same sample source of seawatr at 1.030! Almost a certain death for most organisms in captivity if maintained for a short length of time!
And last but not least, the SeaTest by Aquarium systems. This hydrometer measured the same source water at 1.028, close to the same reading as the previous water.
The results were shocking and probably would turn the stomachs of many hobbyists. A carefully calibrated refractometer measured the water at 1.026. So what's the verdict? I'll let you decide for yourself. As for me, I'll stick with my refractometer.
