These Cartridges come in a 2 pack, and are made to fit the lift tubes of Muti-Pore and Undergravel “E” filters, serving as a replacement for when it’s time to cycle out aquarium filter media. Chemical Filtration: In addition to absorbing ammonia, nitrites, nitrates, and phosphates in a timely manner, these Activated Carbon Cartridges also remove harmful chemicals and toxins, clear up discolorations, and reduce foul odors from your tank. Top-Quality Activated Carbon: These Activated Carbon Cartridges come together in a 2 Pack. For best results, replace cartridges every 2 to 4 weeks. They’re lightweight, disposable, and are safe for Freshwater and Saltwater aquariums. Old School: There has been a burst of growth, development, and ingenuity within the aquatic industry, and although we are a part of this as well, we still provide replacement media for undergravel aquarium setups.