The National Geographic Waterfall Oasis Cartridge is a replacement filter cartridge for the National Geographic Waterfall Oasis Aquarium. The filter helps absorb odors, pigments, and chlorine with activated carbon. Only at PetSmart. Features: Replacement filter cartridge for the 5-gallon Waterfall Oasis Aquariums Includes: 1 Waterfall Oasis Cartridge Intended Pet(s): Fish Material(s): Carbon Color: White Product Dimensions: 5.5" L x 3.1" W x 0.1" H Compatible With: 5-Gallon Waterfall Oasis Aquariums Assembly Instructions/Directions: Rinse the filter cartridge under cool tap water to remove dust. Caution: This is not a toy. Keep out of reach of children. To maintain a healthy aquarium, change the filter cartridge every 3-4 weeks. Remove the cartridge when medicating the water as carbon will absorb medications. Change out 10% of the water weekly or 25% monthly. Use a water conditioner (sold separately) every time you add fresh tap water to your aquarium. Never use soap, detergents or cleaning agents while cleaning the aquarium or equipment as they can harm your fish. Size: Small.