Not saying you can't use a powerhead, but if setup correctly you really don't need it. Here's one of my own that was setup for 3 years. This is all the equipment, nothing removed for the pic. There is a spray bar top left above the disc that you can't see and I only used an Eheim 2215 and this is a 72G (4-ft tank). It is a myth IMO and experience that you need strong flow to move CO2 and dissolved ferts around a 2-4 ft and sometimes 6 ft setup.
, on Flickr