Don't have a clue the cause, I think it was old age. He was 5.5 inches long and a beaut.
No problems with the tank,
Temp steady at 78
Was eating normally 2 days ago and then died today
No signs of disease and a full belly, not constipated because he pooped yesterday. Ate some zucchini 2 days ago and the female in the tank is helathy as ever. No other signs of fish in distress and no neons died so I have to assume it was just his time.
Guess I will have to find a smaller male to try and get the mating I hoped from him.