Lee's 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 & nitrite), 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 nor harm them. Great for fresh or saltwater aquariums up to 40 gallons. Shipping weight: 1/3 lb.