Help! Gold Severum lips protruding, red fin, lethargic, not eating...

My amazing Gold Severum is not well! I noticed 2 days ago that he wasn't eating...usually he comes right to the top of the tank to eat. But on Saturday evening he was just hanging around at the bottom of the tank, facing the Hydor circulation fan. His mouth was open wider than normal, and he wasn't closing it fully. No other symptoms. No visible marks on his body.. just a wide open mouth. He didn't seem to be in distress, just listless and hanging around at the bottom of the tank.

Same thing yesterday, so last night I removed him from the main tank (150 gal) and put him in a QT tank (10 gal) and started treating with Marycin 2 -- research online said might be columnaris and to treat with anti-biotic. That's the only one 1 had on hand.

The tank he is normally in has fine parameters -- just did a 50% water change after i noticed he was acting weird.

This morning, noticed the base of his pectoral fin is red (see pic).

Not sure what this is.... any ideas/advice? I love this fish and would hate to lose him. I can get to the petstore tonight to pick up different meds if need be...


Thanks!

Here's a before & after photo... the biggest concern is his wide gaping mouth -- protruding lips. Still no visible growths on his body.... my husband noticed a bit of white cloudy stuff coming out of one gill, but it's gone now...

Well, my lovely Severum has died. I still don't know what was wrong with him. He never developed any other symptoms except his lips opened wider than normal. His red fin even got better. So this is a mystery. And very sad... I'll miss him