I switched to Purigen running 24/7 after using Marineland's Black Diamond GAC
24/7. Can't say I've noticed any difference, good or bad. I switched because (1) you can regenerate Purigen, and (2) I was worried about GAC
stripping the "good stuff" out of my water, along with the bad. Supposedly, according to Seachem, Purigen targets only the "bad stuff" and leaves the "good stuff" in your tank. I have no way of knowing if that's true though.