Red Oscar

Question
I have one oscar set  up in a 55 gallon tank.  He is about 9 months old.   I first got him when he was about 1-1/2" long and now he is about 8"  long.  I have in the past 3 months moved him into this 55 gallon tank.  He was in a 20 gallon long.  Once I moved him he started acting stranger than a normal oscar acts.  I have had oscars before but they never acted like this.  He will all of a sudden just dart around the tank banging into ever thing including the filters leaving gashes on his head and sides.  I noticed his eating has slowed way down to almost nothing.  I noticed some spots on his head and went to the pet store and got some meds for hole in the head.  His head looks a lot better.  I just did a water change tonight.  I replaced the filters as well. I was in the other room about two hours later and heard a lot of gravel and noises coming from the tank.  I went in and turned on the lights because I was on my way to bed.  When I did I went over and looked at him and he has marks on his side and a big gash on top of his head now.  What makes them just dart around and act strange.  I know that they are heavy sleepers and turning on the light can scared then causing them to act strange but it was dark and no one was in the room when this happened.  I worry about him not eating and the strange behavior.  Please let me know what is going on.  I just checked the water and it is the right PH and all the other levels.  Something is not right and I want to make it right so he can live a long life.

Answer
Hi Jimmy,
  One of the main causes of fish darting around the tank is when the ammonia level is too high.  You said you "did a water change", but how often are you doing this?  You should be changing 25% of his water once a week, every week to keep him happy and healthy.  Have you been doing that?

-- Ron
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