Pristine is not used in a reactor, it is introduced directly into the tank and the bacteria reside in the water column, substrate, and the biological filter.
I use Purigen in a custom made reactor. Seachem sells Purigen in loose form or in a bag that is placed in the path of water movement. The loose form is cheaper than the bag form. Also, the bag tends to compact the Purigen beads and blocks water flow thru it.
Here's a link to details on my reactor:
http://forum.simplydiscus.com/showth...urigen-Reactor
Here's a link to my complete filtration system:
http://forum.simplydiscus.com/showth...tration-System
Here's a link to how my filtration system functions:
http://forum.simplydiscus.com/showth...stem-Functions
Also contained in one of the links above is a description of how to modify a HOB reactor to hold Purigen.
Hope this is helpful.
Paul