Round Cobalt Blue Marbles - 5 Pound Bag for Aquarium Decor and Decorative Use 5 pound bag contains approximately 400-500 Marbles. Will cover approximately 125 Square inches. Fills up a 5" cube vase. Perfect for Aquarium Use or Decorative Vase Filler. Commonly used for centerpieces. This item will sink water and reflect light. Some marbles may have slight imperfections.