Marina I25 Internal Filter is a compact yet powerful internal filter that easily clips onto the Marina goldfish aquariums or can fit any other goldfish or tropical tank that is up to 6.6 gallons with its secure suction cups. Since its motor is submerged in water, it is exceptionally quiet. The Marina i25 comes complete with one power cartridge that is uniquely designed to enable the water to enter the center of the cartridge for an effective mechanical, chemical and biological filtration process. Upon entering the center, the water first enters the zeolite chamber so toxic ammonia gets removed. It then enters the second chamber which contains the carbon so that pollutants and odors get eliminated. The floating debris then gets trapped inside the cartridge, all to ensure your aquarium water is crystal clear.