Bettas can and will kill guppies. Usually bettas are kept alone because their aggression or in pretty big tanks with other not other big finned fish idk what kinda guppies you had typically feeder guppy are your safest type of guppy to pair with them. some of the other fish may have got them too as guppy are not typically aggressive.
Great job keep it up.
Those sharks might have been the culprits to why those fish died. They can be some aggressive fish alot of times.
Bettas can and will kill guppies. Usually bettas are kept alone because their aggression or in pretty big tanks with other not other big finned fish idk what kinda guppies you had typically feeder guppy are your safest type of guppy to pair with them. some of the other fish may have got them too as guppy are not typically aggressive.