I've had a veiltail named Veil for the past year and a half. About two months ago he contracted some finrot that ate about half his tail away. I dealt with the problem with the recommended salt quarantine treatment and it worked just fine seemingly. His fins started growing back.
But they stopped about 3/4 of his original tail length. I figured, ok, he'll just have shorter fins now.
During the sickness he also lost a lot of color and never gained it back despite otherwise being back to normal. I figured, ok, he'll just be a short finned silver fish now; as long as he's happy and healthy I'm good.
So about a month ago I would say he was back to normal other than being gray and having short, but otherwise healthy fins (maybe a little stiff but not clamped).
Well today he's no longer alert, sits at the bottom of the tank, and when I threw a pebble in front of his face when he came up for air he took it but then spit it back out and sank to the bottom of the tank. Seems like symptomes of a cold tank but my whole house is 80 degrees, his neighbor is perfectly active (his neighbor has always been kept in identical conditions and is the same age) and the other divided tank's 2 residents are all good with the temperature and almost identical conditions (I do nothing different but it is a different tank). Ammonia, Nitrites, and Nitrates all stayed clean (I test weekly). He also seems to swim in short bursts, as if it winds him and just sinks, not swims, but sinks to the bottom tail first.
Any thoughts? Was his immune system just too compromised to deal with whatever the problem is now after that finrot episode a month back? What could general lethargy and loss of appetite mean in warm environment?
Pics for visual reference. The first is him currently. Gray. He changes from light to dark gray depending on the day of the week.
The second pic is him just after adoption. He looks a lot like he did as a youngster now, oddly enough.
The third pic is him at what I would say was his prime. Long tail and bright colors.
The last pic is just of his house. There's a whisper 5-10 gallon filter behind the dividers.