fierce puffer

Bought 2 plants, 2 more ottos and 4 female bettas (on the cheap) from Vista Point fish shop. Placed them in the same planted tank with my puffer and my fierce puffer starts to bite all of them! Although the bettas bite back sometimes, they are no match for the tiny puffer. I had to isolate the puffer in a breeding cage for baby fish. One of the female betta's developed a nasty fin rot. I wonder was that due to the injury inflicted by the puffer?