This was exactly what I experieced with my first betta and a couple of shrimps, red cherry, in a 8L tank! My current betta is fine with shrimp, but I put tat more down to the fact they are much harder to see being culls, they are brown or clear, and the tank is bigger 25L with a lot of plants etc!
Again this was my first experience. Second and third didn't do much better (no pun). The last and current have been plain saiing thanks to JayC assistance which is on here under Betta subject! Good luck with the breeding Crabby, I think I have said before, I bought 3 female (?) betta from a closing store but one must have been male as I ended up with about 50 babies (I did think the fish were quite aggressive but dismissed it, should have been a clue????) - it came to nothing as I am housebound so couldn't deal with it in time, the only good part about it was it made me adament I don't want to breed them ever again..................
I plan to go through this whole thread later, haven't yet, got to do some housewor first, d'oh! Still, something to look forward to later.
Simon