Underwater Treasures Bubble Disks create life-sustaining bubbles for active fish and a magnificent aquarium. They circulate water while generating much-needed oxygen for your aquarium and all its inhabitants. The size and output of your air pump will establish how large a portion of the disk will discharge air bubbles. Rinse the Bubble-Disk in clear water to remove any dust. 4.5" diameter. 4.5" dia.