no there is no adjuster. My local petshop has advised that I need a "wispa" pump which are supposed to be quiet. I dont run the pump constantly as its too annoying!!
Wrong again wildwood. If diaphram pumps weren't designed to run flat out, they'd either tell you about it or people would stop buying them. I've been running diaphram pumps for 35 years and i never restrict them....you need to try keeping rabbits or something and stop keep dishing out bloody awful advice on aquarium based things.
I bought a tank in Wilkinsons for �15 with pump (which is outside of tank). I just checked it was working, yes.....bubbles flowing.....but can't hear it. I can hear the tv so am not deaf! (can also hear my tinnitus though!