1 dozen contains 12 balls.
Packaging of this item might be in a nylon bag because we share per kg from a larger sack.
The bio balls helps to trap living/ micro organisms so it dosnt over crowd the pond/ aquarium. It is basically a place where living organisms can live. They are trapped as water recylates. It can be used inside a filter or just dropped inside an aquarium or pond.
It is an effective way to control growth of algae etc in the pond/ aquariums.