Maybe some fish just don't last anywhere near as long as potential lifespan listed. Over a week ago he was perfectly fine and had greedy appetite and was normal. I've not lost any juveniles or babies to sudden death/infection in the same conditions at all. Confusing and frustrating. Like hitting a wall all of a sudden. There's no long drop-off, just sudden infection and rolling over.
SAME situation with all my acaras, perfectly fine and healthy into adulthood then developing all kinds of costly health issues and rollover.