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Both these Acropora spp in the
author’s reef tank show healthy polyp extension. Healthy polyp extension is a good
indication that delicate species like Acropora are doing well. |
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Recently, a situation developed in my reef tank that
reminded me of my own words spoken to aquarists a number of times in the past. Many times
in the past I suggested that careful observation of his/her aquatic guests is extremely
important; in fact, when it comes to their well being it is perhaps the most important
skill to acquire. Testing water quality with test kits is important, but is secondary to
observation. This of course recognizes that there is a vast difference between the
observational skills of an experienced aquarist compared to those of a beginner. The
experienced aquarist knows what to look for, the beginner doesn’t. How early we are
able to recognize a deteriorating situation is critical in a reef tank, because many of
the sessile animals are very intolerant of certain changes to their environment.
The truth of this was brought home to me recently when an
out break of RTN (rapid tissue necrosis) began to develop in my reef tank. Tissue
sloughing off of some of my more delicate Acropora spp was a clear red alert signal, but
had I been looking more closely over the preceding months I would have recognized yellow
alert signals. Months before I noticed, but didn’t respond, to the fact that some of
my old clams were not opening fully, and that my 15-year in captivity E. ancora was
not extending its polyps as it did in the past. I even noticed that some of my SPS corals
were closed, not extending their polyps at all. However, the fish were fine and most of
the corals seemed happy. I tested for nitrates, orthophosphates, alkalinity, calcium, and
a lot of other things, but everything appeared within normal reef tank water parameters.
And, it was time to do my 20% water change, so I mixed up almost 200-gallons of new
seawater and made the change.
Within two days of the water change RTN made its
appearance. So, thinking something was wrong with the new seawater I tested it for
impurities, but found nothing. Finally, I had a revelation, and tested the one thing I had
ignored for many months - salinity. Both devices I had gave me a specific gravity reading
of 1.032. It is my custom to change 20% of the seawater in my system every other month,
and due to an error in the way I was changing seawater the specific gravity of my
system’s seawater was rising, and stressing the animals most sensitive to high
salinity. It is very important to recognize that different animals have differing
thresholds in their responsiveness to changing environmental conditions.
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