Air pumps are a great addition to any aquarium. Providing circulation and oxygen to the fish is a vital function. Air pumps however do make sound by the vibration they use to create the air pressure. By using an oversized pump such as the AP-50 on a 20 gallon aquarium, you can quiet the sound by having the control valve turned down. Alternatively this pump will scale with you when you upgrade to a larger aquarium. The AP-100 is very similar to the AP-50, except is has two outlets and more air pressure. If sound level is your primary concern, review the USB Nano Air Pump.
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