Sorry for not responding sooner...Purigen is like GAC
, but it's a resin that supposedly absorbs more of the bad stuff and wont leach it back out when all used up. And, you can recharge it by soaking it in a bleach solution, then in water with a dechlorinator.
I get mine from the good Doctors:
CD-21412 100 ml. w/ mesh bag 3-pk $18.79
I just put one bag in a high flow area of the filter. I replace with a fresh one monthly. I toss em' Cant be bothered with the whole recharging thing.
I also use 1 unit of Chemi-Pure Elite that I replace bi-monthly. Pretty much the same as purigen with some added benefits (supposedly).
Do they do anything besides drain my wallet? ...I don't know, I just know my critters are healthy and water is in good shape.