HELP! Is my Neon being Attacked?

I came home to one of my Neons slowly dying with the only noticeable being its raw/pinkish tail. My water is fine, the other 10 are doing fine. Also my tank has been cycling for several years, so it can’t be new tank syndrome. He’s still barely alive, so is there something I can do?

I came home to one of my Neons slowly dying with the only noticeable being its raw/pinkish tail. My water is fine, the other 10 are doing fine. Also my tank has been cycling for several years, so it can’t be new tank syndrome. He’s still barely alive, so is there something I can do?