The outside of the power cartridge features polyester foam to trap fine particles; while the inside chambers contain carbon to remove pollutants and odors; and zeolite to eliminate toxic ammonia for a cleaner, healthier aquarium environment and crystal clear water. The Bio-Screen, with its large surface area, is designed to promote the growth of friendly bacteria. Enhances aquarium water quality. Bottom positioned motor for quiet operation. Waterfall spout for continuous oxygenation. Effective 3 stage Filtration (mechanical, chemical, biological). Bio Screen provides large surface area for growth of friendly bacteria. Easy replacement of Power Cartridge. Compact size and energy efficient. Refill Power Cartridges available (A308, sold separately).