I mentioned avoiding the pellets only because granular activiated carbon (the one with irregularly shaped peices) has a larger surface area and is therefore more effective. Other things work into that as well such as pore size. A good quality GAC is Marineland's Black Diamond. You can get a knock-off at PetSmart and Wal-Mart too for a little bit less money.
Because you have a refugium with macro, you probably dont need a PO4 remover. Pretty much all the other chemical medias I can think of (Chemi-pure, Purigen, etc) all do a similar thing as carbon although not usually as effectlively so they are probably unnecessary as well. So I dont really know what else you would want to run with the carbon... have you considered running a phosban reactor with carbon instead of the canister filter?
http://www.championlighting.com/product ... ctid=17145
You can usually find one used on one of the larger sites like rc.com and they do a good job of fluidizing the media. You can run it with pretty much any of the larger particle-sized chemical medias and it only requires a small pump like a minijet 606.
BTW. check out this link for more info than you ever wanted on GAC>>>
http://forum.marinedepot.com/Topic60238-14-1.aspx
I hope that helps... :neutral:
Jesse