Argh. Please, please, please get a new hobby that doesn’t involve any living creature. If you don’t somehow manage to kill your fish (or end up with some virulent strain of bacteria to do it for you), then you “lose” them. Unless the last time you fed them was a month ago, two amano shrimp did not kill and eat a betta in two days, period. Maybe ID could eat a whole betta–bones and all–in two days, but that would be a lot to expect from even his 4.5″ (plus chelae) self, and unless he was half-starved, forget it. Two shrimp pellets and his tummy is quite completely full for a day.

Get a new hobby. Collect stamps, or some kind of anime trading cards, or take up bicycle repair, or start a mould colony. Nobody cares if mould dies. Anything…just stop the fish-killing! Some people are meant to keep live animals and some are not. You are not.