The Vortex reactors use a Rio50 powerhead/pump.
Something you might wanna try out though, is a maxi-jet with their venturi adapter. These make really fine bubbles for a SW protein skimmer. You could run your CO2 into it and it would enter the gravel vac 'chamber' as tiny bubbles, making for a lot faster diffusion. That means you could have a shorter gravel tube length....less tank clutter.
I'd go with a small maxi jet, like a MJ300, and the venturi adapter is $5 extra.
this is something I want to try too, but not until I get my new light canopy built..the old one is just too heavy to remove by myself, and has design flaws anyways. I have the spare venturi adapter, but no small MJ powerhead.
I did run this by Tom Barr,and he said it should be a much more efficient design than just whipping a larger CO2 bubble around.