The Dual-Action foam filters are biological filters composed of open-celled foam which provides enormous amounts of usable surface area for beneficial bacteria to colonize. This bacteria breaks down harmful waste substances (ammonia and nitrate), making your aquarium a safer environment for your fish to live and breed. This fundamental filter is excellent for breeding all types of aquarium fish, as well as for hatching and raising brine shrimp as it will not trap or harm them. Replacement foam filter pads are also available. Packaging Blister card.