Review on Boxtech Super Quiet Aquarium Air Pump - Long-Term Quietness, Adjustable Air Volume & Oxygen Pump for 1-150 Gallon Fish Tanks by Teresa Presha

I expected the sound to be louder but actually it's pretty good. if you need absolute silence to sleep, I would look for something else, but this suits me perfectly. I've run it on two 5 gallon tanks and it works much better than the small round ones I've used before. The small round ones are the quietest I've used but they aren't very durable and if you get even a little splash on them their air pumping power decreases. it comes down to preference. My little silent round air pumps are good and I may use them again for bubbles in the future but for now I'm glad I have them because the water looks cleaner now.