jaguar cichlid

tank size : ~ 450 liters ( ~100 gallons ) tank age : 4 years pH : ~ 8 nitrite : 0 ppm nitrate : ~ 40 ppm kH : ~ 12 gH : ~ 10 tank temp : 27 celsius ( 80 fahrenheit ) My 4-year-old male jaguar cichlid hasn't shown interest in food since July 12th. He seems to be in perfect shape other than that...