Refractometer vs. Deap Six swing arm hydrometer

  You are now enlightened grasshopper.

I had 2 deep 6 hydrometers for a while and they tested the same water different by .06 degrees.

If not cleaned regularly salt deposits can build up on the swing arm and cause readings to be off.  Those deposits will not dissolve when the water is tested again a week or two later.  If left long enough I suppose they might, but typically we draw water and take a reading rather than drawing water, waiting 30 minutes and then taking the reading.

When my mom got her first tank it came with an old swing arm hydrometer.  Thinking it would of course work properly we used it to test the salinity.  Corals lived in the tank very well, but fish just kept dying.  After several weeks she got a refractometer and tested the salinity to find that it was 1.35, way too high.  We fixed the problem and the next few fish lived a long happy life.

I went 10 years before getting a refractometer for myself and only got it recently because my cousin was selling it.

Shane has done this long enough. I believe him. Seriously.

Of course anything from 1.020 - 1.028 is within the totally acceptable range. We should not get too worked up about salinity. From my experience, there is no perfect.
I often taste the salinity of the water that comes with a fish or coral. That tells me whether I have a 10 minute or a 20 minute acclimation period.
After calibrating a Hydrometer just once by comparing it to a true correct value, if it's kept clean by rinsing in freshwater after each use and a vinegar bath every 3 months or so, it will be accurate for the rest of your life.
BTW, You can make your own calibration salt solution and calibrate anything by that, refractometers included.

6.20 grams of sodium chloride, and 161.00 grams of RO/DI water = 1.028 specific gravity

OR

Salt mix containers [used to] say what salinity the resulting mix will be if salt to water proportions are used exactly as instructed. The one I just looked at says 1/2 cup to one gallon should be used but still should be checked with a meter. I find it interesting that this salt company recommends fish are best kept at 1.021-23 and coral at 1.021-24. I would assume that their 1/2 cup/gallon of water puts the sg within that range.
Some of us old timers mix up salt water in that way and only rarely bother checking it. A little variation is no big deal.


Edited by Mark Peterson - November 01 2010 at 10:02am

Lewy instructions are for sissy's!  Mark there is no way this lazy reefer could get anything that exact. But still good info to know. File that one away in the might be useful one day section of the brain.