I need help! I'm looking in to getting a new air pump because the one I have (Aquatop AP-40) is EXTREMELY LOUD. I currently have it running a small air pump in my 5 gallon tank. I've been looking online but I'm very confused as to what size I'd need. I would like the pump to be adjustable and quiet (preferably under 30 decibels). Do you have any suggestions (also what does AP-40 mean)?