The Fluval Q2 air pump is a very quiet and powerful unit. When I first plugged it in I thought it was not running it was so quiet. It is big but not to big. It has variable output and produces constant air flow. It has a swing arm and diaphragm design. It is also double walled and has rubber feet. It is also very well built and feels very sturdy. I paid $35.20 I got 20% off due to a big sale at my LFS. I give it a 9.5 rating. I have a Rena air pump on my 45 and I like it but it is not as quiet as this pump.