Fliter Media Question

[MMAX]

I have a Fluval 305 cannister type filter on my 20 gallon. It contains 2 foam pre filters, 2 carbon packs on the bottom tray, 1 carbon pack and biomax ceramic rings in the middle and the top are biomax ceramic rings. I was told by the salesman to run the carbon while the tank is cycling but to remove it when you add animals because they need nutrients that the carbon may remove. I took the single carbon pack out of the middle tray and put a foam pad in its place but still have both carbon packs in the bottom tray. Any comments or suggestions on carbon filtration or any other type of media I should be running in my filter would be greatly appreciated.
P.S. I've also heard of taking all the media out of the cannister (foam pre filters and all) and putting in live rock. Comments on this?