Tetra barbs die within 4 days of purchase

It appears that tetra barbs are not suitable for a fish bowl
A pair of tetra barbs were purchased from an aquarium for Rs 50.
3 days later one tetra barb was found floating in the fish bowl.
The dead tetra barb was removed.
However the next day, the other tetra barb was also found floating in the water bowl
Compared to the gold fish, guppy bowl, the water in the bowl was fairly clear, yet the fish died.