well with some research I read that over eating blood worms could do it to certain fish as well and this guy was (yup was, he finally died) in the same tank as our puffers and loved munching worms. I always fed him flakes first but he still would gorge on worms.
What stinks is we replaced him with an identical guppy and it lasted one night. Must have stressed out and I found him up cought in the filter intake.
Checked water levels and everything is perfect.
Just bad luck I guess. Im hoping its not some parasite as a few weeks ago I had my goby in the tank finally pass. He stopped eating tho. This guppy never ever skipped a meal. The GF was/is pretty upset about it.