Neon Tetra, not doing well…

I have 4 tetras and a spotted Cory in an established 9 gallon heated, filtered tank. They’ve been doing well for a few years. Now one of the tetra is not doing well and I don’t know if it’s just getting old or if it’s just sick and I can help it somehow. For the past couple days it hangs out away from the other fish and it’s head is constantly tilted up at a slight angle. It’s belly has started sinking in and it’s gills seem slightly flared out. When I feed them it goes after the food but spits it right back out, which is unusual. They’ve eaten the same food their whole lives with me and never done that before. The other three fish have started getting somewhat aggressive towards it. Maybe because it’s in distress and they don’t like it? These guys are at least 3 years old by now which seems to be a good run for tetras these days. I guess my question is, do you guys think I should try some kind of medication? Do you think it may just be this guy’s time? Or??? I’ve experienced swim bladder issues before and that’s not what this seems like to me. I don’t feed them live or freeze dried food so I can’t imagine it’s parasites. All the plants, rocks, etc. have been in there for at least 2-3 years. What else could it be? See pictures.

I'd say old age and not a lot you can do.

euthanise it

Colin_T said:

euthanise it

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I’ve struggled with that if it doesn’t get better. Especially if the other fish are being more aggressive and stressing the tank out. What would be the most humane way?