top fin retreat filter large, if-s (2 count) top fin 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. features: helps absorb odors, pigments, and chlorine with activated carbon, easy to change includes: (2) filter cartridges intended for: top fin filter size: 4.3 in l x 2.3 in w x .75 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.