Keep your aquarium clean and healthy with Top Fin’s Element Filter Cartridges. These cartridges help absorb odors, pigments and chlorine with activated carbon. It’s a great way to keep your aquatic friends happy and safe. Only at PetSmart. Features: Helps absorb odors, pigments, and chlorine with activated carbon, Easy to change Includes: (2) Filter Cartridges Intended For: Top Fin Element Filter Size: 2.1 in L x 1.9 in W x 3.7 in H Instructions: Rinse the filter cartridge under cool tap water to remove dust. To help maintain a healthy aquarium, change the filter cartridge every 3-4 weeks, or if water flow becomes obstructed. Remove the cartridge when medicating the water as the carbon will absorb the medications. Change out 10% of the water weekly or 25% monthly. Caution: This is not a toy. Keep out of reach of children.