I have been playing around with Brightwell Aquatics XPort PO4, which is kind of like a crouton version of GFO, but 'ultra' high capacity and not requiring fluidizing. I am down to using half the recommended dose of the same amount of HC GFO and after a couple of months am still getting Hannah PO4 readings near 0.00-0.03 with daily feedings of Reef Snow, various other (non-rinsed) foods for the fish and periodically coral frenzy and reef roids (very high in PO4) and ATO with RODI.
In terms of food rinsing, Randy HF recently wrote an article that covered sources of PO4 in the aquarium and concluded PO4 sourced from most (or maybe all) frozen foods were the major contributor to PO4 but rinsing did NOT reduce PO4 by any significant amount:
http://www.advancedaquarist.com/2012/3/chemistry.
I am happy with the XPort PO4 product but don't see why using more GFO wouldn't accomplish the same goal. I have some extra if anyone around Nanaimo would like to give it a try.
Dan