Lee's Dual action Goldfish Foam Filter provides increased surface area to establish more beneficial microorganisms which break down harmful wastes and bacteria, resulting in a cleaner, healthier environment for your fish. The one-piece airlift system draws water through the sponge filter very efficiently. The Dirt Magnet offers a variety of uses for your aquarium. It is a great tool for seeding new fresh or salt water tanks. It is a beneficial filer for quarantine tanks because it won't remove medications and it is easy to use. Gravel is not necessary for this filter so it works well for bare bottom tanks. The Dirt Magnet is safe for hatching and raising brine shrimp because it won't trap or harm delicate brine shrimp or baby fish. The filter also helps plants by turning fish waste into valuable plant food. The Dirt Magnet is available in four sizes. . The round Junior filters tanks up to 10 gallons. The clover Goldfish filter is for tanks up to 125 gallons. The square Hatchery filter is for tanks up to 35 gallons. Info from the Aquarium Guys