Planted Tank Guru
Join Date: Jul 2010
Location: British Columbia, Canada
You can add the Purigen at any time - now, or when the tank is cycled and you get fish - doesn't matter.
Purigen picks up a lot of impurities or other unwanted material, assists in removing toxic material, or neutralizes conditions that develop toxicity, but doesn't adversely affect plant nutrients to any discernible degree.
I've used it for years in my planted tanks.
Go for it.