strange behavior from my tiger oscar

Question
I 'inherited' an aquarium from my father-in-law so I don't know exactly how big it is but I'm guessing it's about 50 - 55 gallons. I have a crappy hang-on-the-back filter that doesn't do nearly enough but I can't afford to buy a new one right now since I am unemployed. My husband gave me a tiger Oscar Christmas before last. He was about 4 inches and had great coloring. Now, he's about 12 inches. His color is still good but changes occasionally. He has taken to doing something kind of strange and I don't know how to react to it. I was watching my tank one day when Ozzie #yes that's his name# was kind of laying on the bottom at an angle. Not all the way on his side - just tilted. All of a sudden, he "sat up" and shook his head like a dog shaking off water. It was funny and I laughed but he's done it several more times. Today, several times, he has shot to the top of his tank, splashing water everywhere and just generally making a mess. He hasn't jumped out because I do have a lid on it but it's still kind of disturbing. He also hasn't been eating like he used to. He will get excited when he sees the bag that his food is in (he gets pellets - only thing he will eat - I've tried lots of different things) but when I actually drop a few pellets in, he just looks at it and swims away. Is this all normal? Do I need to push the panic button that my Ozzie is sick?  I would really hate to lose him...he's kind of become my 'buddy'.  Thanks so much for your time!

Answer
Hi Toni,
  His behavior fits the symptoms of deteriorating water quality.  Are you doing regular weekly water changes? You need to change 25% of his water once a week, every week to keep him happy and healthy.  

-- Ron
  rcoleman@cichlidresearch.com
  Cichlid Research Home Page <http://cichlidresearch.com>