The super quiet Whisper in tank aquarium or terrarium filter that is ideal for 20-30 gallon tanks. The Whisper in tank filter is easy to conceal inside your aquarium; hide it behind a plant or other decorative object and from the front it is practically invisible. Space-saving design can be flush with the wall and operates in as little as 2 in. of water, making it ideal for low water level environments like amphibian aquariums, terrariums or turtle tanks. Complete 3-stage biological, chemical and mechanical water filtration is provided from the same Whisper Filter Cartridges used in the famous Whisper Power Filter. Whisper Filter Cartridges contain precisely the amount of activated carbon and filter mesh area to provide superior aquarium filtration. UL listed. For more info on Internal or Submersible Filtration, please see Internal Aquarium Filter Basics.
It barely makes a sound and works wonderfully! I use it for my turtle (who makes quite a mess) and this keeps the water clear and smell-free. The only downside is the support, because it can be knocked off the wall of her tank so easily, but it shouldn't be a problem in a tank with only fish and gente-er creatures.
I highly recommend buying it despite of that.