I've had a pleco in a 10 gallon tank for about 7 years.  He moved a few
times with me, and never complained once.  He grew to be about 5 inches
long.  He subsisted mainly on tank alge and an occassional zuccini.
I thought it was strange when he started to get a white film on the
middle of his back.  It was even stranger when he didn't attack the
zuccini that I put in the tank.
Turns out he was dead.
R.I.P.
On the bright side, I can finally tear down the little tank and give it
a thorough cleaning.  I'm not sure what to put into it this time.  I've
always liked having an Oscar... (the last one committed suicide and
jumped out :( )
--- Platinum Xpress/Wildcat! v1.3
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