dat not eating and sitting in the corner

I have a 4" AT, he has always been the punk of the tank, first to eat, and start a fight. For the last week he has just been hiding behinde the drift wood, he is rubbing on the one side and keeps opening his mouth. Not labored breathing, but more of the typical yawn. I just caught him looked into his mouth, and gills. Nothing visible in the mouth,gill plates look nice and red. No visible signs of parasites. Raised the temp in the tank, salted and added stress coat to help him recover from being stressed. Anybody have any ideas? Id hate to lose this guy.
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No I haven't changed anything. The only thing that was changed was by a loach,uprooted one of the plants. If he did get his ass beat, he had it coming to him but I doubt that happened he is the biggest one. I have never seen him get whooped on. I guess I'm concerned cause he keeps rubbing on the left side,and because he was so easy to net. Normally it would take quite a bit of time to do that.

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Everything looks good, nitrates are at 5ppm, my ph is sitting at 7.5. Ammonia doesn't register. Did a 100gal water change about 3days ago on a 210gal tank.

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And the rubbing is almost a constant, he has 3 3" NTT's for tankmates, I've seen them rub on occasion but not as much as he has been doing.

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