betta + shrimp = recipe for disaster
In this equation it's never about IF, it's about WHEN. Betta will one day figure out that those little red things swimming around are TASTY, then it will eat them all.
I had a betta, calm as could be, lived with a bunch of cherry shrimp for 6 months, then one day, no more shrimp in the tank, and a very dead and gorged betta. He ate himself to death. But he won the war, he eliminated every baby, juvie and adult in the tank!