Marina i25 Internal Filter. The Marina i25 is a compact yet powerful internal filter for use with Marina goldfish aquariums or any other goldfish or tropical tank up to 25 liters (6.6 US gallons). It effectively filters water through 3 stages of filtration, providing a cleaner and healthier aquarium environment. The filter's uniquely designed Power Cartridge (included) enables the water to enter the center of the cartridge for an effective mechanical, chemical and biological filtration process and exit from the polyester foam layer leaving all trapped debris inside the cartridge, ensuring your aquarium water is crystal clear Key Features : Enhances aquarium water quality Ideal for goldfish or tropical tanks up to 25 L (6.6 US gal.) Bottom positioned motor for quiet operation Waterfall spout for continuous oxygenation Effective 3 stage Filtration (mechanical, biological, and chemical) Easy replacement of Power Cartridge Compact size and energy efficient Refill Power Cartridges available (A134, sold separately)