It's more likely that the balloon mollies died because they have a similar size and shape and finnage as either a male or female betta. Some bettas are more prone to aggression than others and with some if it even looks like a betta, they'll flare and get mean with it. I had one red female betta who would flare at my guppies and then present herself as ready to mate with them!!! O__O;;
One specific set of rules DOES NOT APPLY to all bettas. It's a hit or miss. Responsible betta breeders are trying to breed out aggression in this species with mixed results... and you can bet those 'mixed results' trickle right down into the pet trade. Because obviously you sell of that which you don't find desireable or don't intend to keep for your own breeding agenda. Hence, some bettas are docile as kittens... others are more easily provoked.
So it's best to say that bettas should be treated with kit-gloves when it comes to introducing them into community aquariums. Most don't have a problem with it as long as they can have some space to call their own, but it's always best to keep an eye out just in case he doesn't play well with others.
I speak from much experience on the matter.
One specific set of rules DOES NOT APPLY to all bettas. It's a hit or miss. Responsible betta breeders are trying to breed out aggression in this species with mixed results... and you can bet those 'mixed results' trickle right down into the pet trade. Because obviously you sell of that which you don't find desireable or don't intend to keep for your own breeding agenda. Hence, some bettas are docile as kittens... others are more easily provoked.
So it's best to say that bettas should be treated with kit-gloves when it comes to introducing them into community aquariums. Most don't have a problem with it as long as they can have some space to call their own, but it's always best to keep an eye out just in case he doesn't play well with others.
I speak from much experience on the matter.