The Top Fin 4-In-1 Filter Cartridges IF-S come in a convenient 2 pack of 2, providing a total of 4 cartridges for your aquarium. Designed for 20 gallon tanks, these internal filter cartridges are specifically made for fresh water systems. With the Top Fin brand known for quality and efficiency, these cartridges will help keep your tank water clean and clear. Perfect for aquarium enthusiasts looking to maintain a healthy and vibrant aquatic environment.