Possible fish disease

Question
I have a 55 gallon tank with a variety of fish.  The fish that appear to be ill are one mono and one serpae tetra.  They have been turning black over the past day or two.  They seem about as active as usual, but not eating as well as usual.  The mono has lost his shine - where he used to be silver her is black near his tail fin.  The tetra just has black mixed in with his usual orange color, but doesn't look good.  Any help you can give is greatly appreciated.  PS - the water tests within acceptable ranges on all elements.

Answer
Hi Gwyn,
 Hmmm...  its really hard to say.  Turning dark can often be a sign of general discomfort which might be brought on by either being chased alot or by deteriorating water conditions.  I know you said the water tests were good, but if it were my tank, I would do a 20% water change.   (I generally recommend that people do a 20% water change once a week, every week, to keep their fish healthy).

-- Ron
  rcoleman@cichlidresearch.com
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