Odd Oscar Behavior - Breathing and Spaced Out

[quikv6]

Have you tested your water?

Yes

If yes, what is your ammonia?

0

If yes, what is your nitrite?

0

If yes, what is your nitrate?

5

If I did not test my water...

1. ...I recognize that I will likely be asked to do a test, and that water tests are critical for solving freshwater health problems.

Do you do water changes?

Yes

What percentage of water do you change?

71-80%

How frequently do you change your water?

Every week

If I do not change my water...

1. ...I recognize that I will likely be recommended to do a water change, and water changes are critical for preventing future freshwater health problems.

Adult Oscar (5 years old) hasn't eaten in 5 days, and is exhibiting odd behavior. Rapid, Rhythmic breathing and gill movement, and an overall spaced out look, where he is just swimming in place and not responding to any stimuli. The breathing isn't heavy, but it is faster than normal, and very rhythmic. There is a very occasional "cough", and then back to the rhythm. This isn't the typical Oscar sulking. All other fish in the tank are acting normal.

I have done one treatment in the main tank (PraziPro liquid and MetroPlex) yesterday because of this behavior. No change. I don't want to throw the sink at him (or move him) without more specific symptoms. Any ideas are GREATLY appreciated.

Tank/water specifics :

- 8ft 240g, Temp 76-77. 3 FX6s and 3 sponge filters. Water change schedule is 75% every 3-4 days. (Been doing 50% daily since this behavior).
- Ammonia and Nitrite - 0, Nitrates - 5ppm. (Normal is 5-10ppm), GH 50ppm, KH 40ppm, PH 6.7

Thanks in advance!