Tetra Aquarium Whisper, 20-40 Gallon Internal Power Filter Tetra has been revolutionizing and improving fish nutrition since the company's birth in Germany in 1951. Since that time, Tetra has developed one of the most comprehensive bodies of flake fish food knowledge in the world. A full team of biologists, chemists, and nutritionists continually study and discover what keeps fish thriving and living long, healthy lives. The Tetra Whisper Internal Power Filter provides an effective combination of mechanical and chemical filtration for cleaner water and healthier fish.