Nano Filter For Aquarium, Betta Tank, Small Desktop, Fresh Water & Saltwater Aquariums, And Terrariums Up to Four Gallons In Size - Power Filter Ultra efficient filtration system for Nano aquariums, Betta tanks, and small desktops up to 4 gallons Dual-Stage filtration, mechanical & biological filtration Easy to install, simple to maintain, adjustable flow control Traps micro & macro organic particles & foreign debris. Porous, biological sponge promotes beneficial bacteria colonization This does not fit on round aquarium!!! Promotes a healthy aquatic environment. Consider adding a Betta Log, Betta Leaf Pad, Betta Amazon Sword Plant, and a Betta Fire & Ice Plant for your Betta Fish to enjoy..