GT rapid breathing and stopped eating

[toffee]

My one eyed 9" Green terror male has stopped eating the past few days and today he is breathing rapid and heavy. His mouth almost never close now, I can see the 'inner' teeth open and close rapidly. Other than that,he is as aggressive and showing good color. None of his team mates are bothering him and he still swimming around and looking to someone to pick on.

Any idea what's may be going on?

Some basic stuff:
What size tank is he in?-----> 180g
What type filtration do you have on the tank? ------> overflow+sump
What are your water parameters? -------> gh=300, KH=80 pH= 7.2 no3=40, nitrite=0, nitrate=40
What are the tank mates? --------> lots of other cichlids and catfishes
How long has this tank been established? ---------> years
Have you added any new fish recently without quarantine? ---------> no
Is he spitting food or just not showing any interest? ----------> not showing interest
What is your tank maintenance schedule regarding water changes and dechlorinator? --------> 50% weekly + prime

Thanks for helping.

 

[AquataHolic420]

i'd say add salt or melafix, but also maybe do 25% water changes evryday for a week or 2.. couldnt hurt... good luck.

 

[tankmates]

What are you feeding him?

 

[Hawkfish3.0]

Lack of appetite and labored breathing are a good indicator of high nitrate/nitrite levels. Water changes... do it.