The Refractometer! Oh, How I Love the Refractometer!
October 16th, 2007 | by Thomas Belknap |Most anyone who starts out with marine aquariums gets a bit overwhelmed by the costs of all the doo-dads that go along with maintaining a proper tank. That being the case, we wait to buy the nifty things until we’ve gotten the hang of the basics.
Ordinarily, I would agree with this concept, but I must tell you that the refractometer is an absolute must-have. We’d been using a hydrometer which, like most hydrometers, was made out of plastic and hence not the most reliable of measurement systems. In fact, we’d been running the tank about .003 high on the specific gravity scale without realizing it. Once we realized that, we resolved to find ourselves an affordable option.
We ended up getting a refractometer on eBay for 20 bucks. That’s dirt cheap, but it’s the exact same refractometer used at our local reef shop, and more than adequate to the task of testing reef water. Generally, they cost about $100 or so, so while there’s no guarantee you’ll get the deal we did, you’ll probably want to do some research and have a look around if you’re interested in being relatively frugal.
Once you have one of these little babies in your hand, your life becomes instantly easier, where water changes are concerned. Hydrometers are, under the best of circumstances, less than exact. The refractometer does not change its reading based on how you hold the instrument and is not affected by bubbles hanging on the needle. The gauge is easy to read and unambiguous.
We use the refractometer downstairs in our little marine lab to test our reserve water, then we double check the water upstairs to see if there is any change to the salinity in the tank.
Water Changes
Which brings up an interesting point you may want to consider: you should regard your water changes as an opportunity to refresh the water chemistry of your tank, not simply in terms of waste from the fishes, but in general. Over time, the water in the tank may evaporate, leaving you with slightly higher salinity than is healthy. Take the opportunity to introduce water with a lower salinity in a water change to help balance out the loss.
For example, if in a 24-gallon tank, you’re running at 1.027, that’s right at the edge of safe water for marine tanks. When doing your 10% water change (we do ours weekly), it might be advisable to introduce water which is at, say, 1.020. (We measure in specific gravity, not PPM. Consider PPM in terms of its upper and lower ranges, which I don’t know) 1.020 is just slightly below the acceptable limit for the tank, but since it’s only 10% of the total water mass, the net effect should be a slight change to the salinity, probably around 1.025, which is optimal.
You could also mix in things like Alkalinity buffers if the tank needs them, but be sure to mix that into only the water you plan on putting in the tank that change! Otherwise, you’ll end up with reserve water that will do your tank more harm than good. On the up side, introducing chemicals that are already somewhat dilute will be less harsh on your tank than dumping things in directly.
