Nice looking betta! Some of them can be picky eaters, what are you feeding? I find mine prefer the floating pellets over anything else. They spit out the flakes and sinking pellets. They wouldn't even take dried blood worms at first.
You might want to watch his fins with that plastic grass - they tear pretty easily and that grass can be sharp. If you see any fin splitting or tearing, I'd look to that as the culprit.