I did some research on this Purigen stuff and it says that you have to soak it in more than just bleach.
Is that really necessary? And do you ever need to replace this stuff?soak for 4 hours with a solution containing 1 tablespoon of buffer per cup of water (Discus Buffer™, Neutral Regulator™, or Acid Buffer™).
http://www.seachem.com/products/product_pages/Purigen.html