Thanks for all the feedback guys!  I've been checking water parameters weekly and they've always been fine.  I use to rotate cleaning the 404 and other two filters monthly, but for the past while its been every 3 weeks and I clean the substrate each time.  Around 30% water changes are done when filters are cleaned.  The question should have been, is there enough mechanical filtration, which I suspected may have been insufficient.  I'm going to gradually replace all the mechanical filtration media, add more filter floss and get rid of the plecoes and probably pink convicts.  
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				First of all the arowanna needs to go, he has already outgrown the tank and IMO needs a tank in the thousand gallon range.
			
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 I do understand your concerns, but I don't think many aro owners have a tank that big  
  