If you're doing a fish-in cycle, I wouldn't use purigen. It's useful for some things (removing tannins) but part of a mature bio-filter is the ability to process the ammonia produced from organic breakdown, along with fish waste, food degrading, overfeeding, and the occasional dead fish.
That said, you don't have to remove it.
I'm a fan of running carbon in a brand new tank for the first month or two, then removing it completely.