First of all I have been in the hobby 57 years . I have owned many air pumps in all those years and filters .Name the brand I had it and some no names .At one time ,in my younger days I had two 55’s ,a 20 long an 2 tens would have more but ran out of room and oh yeah, money. Had an old belt drive piston pump that was always exciting because you never knew when it was going to screw up and drain the water from tank all over house . This Alita 6 is the best of the best . As others have said it is quiet. Hands down the most silent pump I have ever seen. Output is off the charts . Glad I bought the 6 because I don’t know what I would have done with the extra air. In my 55 gal. tank I am running two Ziss fluid bed filters and a LARGE sponge filter,all three are cranking. In my 13 gallon I’m running normal size air stone , another Ziss fluid bed filter and a LARGE sponge. Again all three are cranking . in my 5 gallon I’m running a small sponge and normal size air stone . All cranking . The Alita replaced a Pawfly MC3000 which had real good output just a little noise and built well . The air with the pawfly had to be rationed to run all that equipment . The Alita is not straing at all in this application ,air to spare . It also is built like a tank . I probably am running the fluid beds too high but I have to do something with all that output from pump,to vent it would make noise . You do not hear this pump all you will hear is what is connected to it. Mind you I have only been running this pump a few days but what I am seeing is this pump is getting stronger the longer it runs. Oh did I mention ,runs stone cold . If you buy it I’m pretty sure you won’t regret your purchase. Thanks for listening.