Aquacity Bio Balls 1.25 Inches Diameter for Aquarium Canister Koi Pond Filter (60-PCS) Bio ball diameter: 1.25 inches. Bag size: 8"x 5.5" Provides large amount of surface in small space for beneficial bacteria to colonize. Good for your canister filter or fish pond filtration. Helps produce turbulent flow which help with gas exchange and remove toxins. Can be used in both fresh and saltwater tanks. Package includes: 2 bags. 30 balls each bag.