I really dont know. LoL. I know that i have 2 whisper 10 now and they are noisy. Here's the rundown. I bought a $400 refuge for $150 here on MR. it came with a skimmer. I wasnt looking for one but it came with one. Its a Cpr Bakpak connected to refuge. So it skims lightly and wet. Better than nothing.
So my idea was that if its there why not try to get the most out of it. So i got a limewood air diffuser and hooked it up to a whisper 10 and it makes mmmuch more bubbles. And it lets the intake pump concentrate on water instead of water and air.
But i notice the limewood isnt pushing micro bubbles to its fullest. So i tied in a second whisper 10 i had laying around and now it makes more bubbles but still not maxing out a 2" limewood. And to make matters worse i have a 3"er on the way. :0)
The 2 whispers are noisy! Its not clunk clunk clunk.... but its mmmmmmmmmmmmm. Annoying. These pumps are real old and i thought that maybe something newer would be better.