Marina 100 Aquarium Air Pump - Quiet Oxygen Pump for Fish Tank, Aquariums & Hydroponics - Perfect for Home, Office & Pet Stores

This is a super little pump. Not silent, but very quiet. Quieter than all the rest, and I've tried every brand. Its good for a mid-sized tank. If you've got less than 20 gallons, you may want to go with the 75, which is even a little bit quieter and still puts out enough for a small tank. I've got this 100 in a 26 gallon and a 36 gallon. I've got a 200 on order to see how it works in the 60 gallon. I found the 100 a bit underwhelming in the 60, and I'm still using a Whisper there.UPDATE JAN 2012: Although my first couple of these pumps were really quiet, the rest have not been nearly so quiet. And my original two are no longer quiet either. They are pretty much average noise level as air pumps go. My Whisper 20 is quieter than these Marina pumps. In fact, my Whisper 20 is quieter now in its second year of use than it was in its first year. I saw where Eheim was making air pumps now, but they are not available in America. Since their filters are almost silent, I wonder if their air pumps are too, and if they might import them in the future? Why can't someone make a quiet air pump?--I would happily pay a good deal more for a silent one.