Ocellaris clownfish not eating breathing heavy

I have two ocellaris clownfish both 1 year in my tank. Large female is not eating and breathing heavy. No visible signs of disease. Only 6 fish in 75 gallon tank. No new additions for over 4 month so no introduction of disease or parasites. Any ideas?
Salinity 1.024
Nitrates 0
Amonia 0
PH 7.9
Phosphates 0
Nitrite 0