The Vortex Diatom D-1 Aquarium Filter is the perfect addition to any aquarium. Whether you have a fresh or salt water tank, this filter is sure to keep your fish healthy and happy. With a tank capacity of 125 gallons, this filter is perfect for both small and large aquariums. The Vortex Diatom D-1 Aquarium Filter is an external filter that can easily be attached to your aquarium. It provides superior filtration without the use of chemicals, making it safe for all types of fish.