Bio balls are used to provide increased surface area for benefical bacteria to grow on in your pond filtraton system. Bio balls have a larger surfurce area per cubic foot compared to lava rocks. Bioballs have 44 square feet of surface, Lava rocks only have 16 square feet. Lava rocks are used often because they are cheap and easy to find. The biological filter is a very important piece of your pond fitration system. Replacing the lava rock in your Biofalls filter with Bio balls will increase the biological filters capacity, improving your filter system! One cubic foot of bio-balls only weighs five pounds! lava rocks weigh over 40 pounds per cubic foot. Bioballs will eliminate the hassle of reaching into your biofalls filter to pull out a heavy bag of lava rock. Bio Balls never need to be rinsed off! reducing pond maintanence. In comparison lava rocks do need to be rinsed off because they will clog ruducing the active surface area for good bacteria to grow on. Bio Balls sink, are black in color and fit perfectly inside the black mesh bags that the lava rocks are currently in. These are a must for your Aquascape Designs Biofalls Filter!How many Bioballs do I need? 2 cubic feet of Bio Balls for the mini Bio falls filter. 3 cubic feet of bio balls for the standard biofalls filter. 5-6 cubic feet of bio balls for the Grande bio falls filter. Aprox. 400 Bioballs per cubic foot. 5 cubic feet ponddepot@msn.com Copyright - All World Rights Reserved Pond pumps, Pond Kits and Pondless Waterfall kits, Underwater Pond Lights. Aquaclearer Extreme bacteria and String Algae Buster and pond fish food. Pond Depot provides Do-it-yourself pond kits and Pondless waterfall kits delivered right to your home at great prices! Thank you for shopping at Pond Depot you online pond superstore!