Bio balls are used in fish hatcheries, recirculating aquaculture systems, tropical fish farms, koi ponds, ornamental aquariums, waste water systems, cooling towers, and other commercial and industrial systems due to their extremely high surface area to volume ratio. Bio balls are an excellent choice for packed media filters, fluidized bed filters, trickle towers and more. Made of food grade polyethylene. Each order is approximately 3 Cubic Feet (22.4 gallons) and roughly 2,000 total bio balls. Surface area: 410 square meters per cubic meter (125 square feet per cubic foot).