The Jardin Economy Corner sponge filter is ideal for 2.5 to 10 gallon tanks. They are great filters for Betta fish tanks and quarantine tanks? The flow is gentle and the water is aerated. It is also easy to clean and maintain. I also use one in my 20 gallon long tank. The filter works using an air pump. We use the Tetra Whisper, it is very quiet.
Jardin Corner Filter http://amzn.to/2kTuXGn
Tetra Whisper Air Pump http://amzn.to/2kTlz5t
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