This value pack contains a 12 month supply of EF-S filter cartridges. Top Fin Small Element filter cartridges have activated carbon to help get rid of organic waste, odors and heavy metals. Please replace every 3-4 weeks. Compatible with 1 Gallon Diamond Aquarium, 2 Gallon Sleek Black Oval Aquarium, 2 Gallon Hexagon Aquarium, 2.5 Gallon Bowfront Betta Duo Aquarium, 3 Gallon Black Glass Aquarium, 3 Gallon Betta Bamboo Aquarium, 3 Gallon Backlight Glass Aquarium, 3.5 Gallon Half Moon Aquarium, 5 Gallon Backlight Glass Aquarium, 5 Gallon Split Bowfront Aquarium, 5 Gallon Gentle Waterfall Aquarium.