Spotted mandarin losing weight and fin rot

[Newsmyrna80]

My spotted mandarin has recently started losing weight and his anal fins seem to be rotting. He has been in a 80 gallon for over 10 years so I don't think it's a copepod situation. Plus he has always eaten frozen, pellets, eggs basically anything I've put in the tank. He's still hunting but doesn't seem interested. I thinking he has a bacterial infection. About a month ago I was cleaning the tank and when I wasn't looking he thought he'd check out the hose and got sucked up in it and into the bucket.
I have a QT always set up that has a ton of pods and chaeto in it. If I move him to there what should/could I treat him with?
Any help is appreciated!

 

[Sk8r]

It may be age. We don't always know the age of fishes, but 10 years is respectable for a small fish. I'd recommend just let him r&r with excellent food supply.

 

[Newsmyrna80]

Hey Sk8r! I was wondering if that was a cause. I got him “used” so I don’t know how old he was when I got him. I did get him to eat some eggs so ����. Thank you for your reply!