IMHO, adjusting air input is more useful than being able to adjust water input. Water output, (back pressure, to control water column height) of course, is critical...
Efficiency of today's brushless DC motors, when taking into account the loss of converting AC to DC and back. (Thanks to whoever it was on here that recently convinced me that the DC pumps we're seeing these days are, in fact, VFD controlled AC motors). I really don't believe you're saving anything on your electric bill. Having an oversized pump, with the ability to run at a mid speed setting gives you just one benefit, AFAICS. You can crank it up, if you need to. Are they _really_ providing an oversized pump, meant to run at mid speed, with these DC powered skimmers? I'm not at all sure. My friend has a DC powered Skimz unit... He's ran it pretty much wide open from day 1. A quality skimmer, AC or DC, should have a pump properly sized to run the skimmer in question, right?
I certainly don't see any advantage of his DC Skimz over my AC powered Vertex. Well... I must admit, I like the water outlet adjustment on the Skimz better... but the pump? Not really. Not any quieter, I don't believe it uses less power.... it _might_ add a bit less heat to the water... since much of the heat radiated by the DC system is at the controller and power supply... but I haven't tried to measure it.
On a return pump? Ok, makes sense. Being able to 'dial in' flow rates is an excellent idea. On a wavemaker? I like my AC ones just fine, but hey, I fully understand the desire to ramp up/down flow rates on a wavemaker. On a skimmer? Hopefully, it's 'set it and forget it', right? Once it's skimming the way I want it to, I don't want to have to touch my skimmer, beyond cleaning the collection cup once in a while.
