I have a 37 gallon tank that been running about 2 months. There is 4 med. Gold fish, a iridescent shark, a couple of lemon Tetris, and a pleco. Can not get my nitrite and nitrate levels down and it is always cloudy. I have done 5 half to three quarters water change in the past 2 weeks. I have a fluval 50 filter on it.also have cut down the food by half. Any ideas on why this is happening. Can it be not enough water movement.