Does Purigen reach a point where it should be discarded?

I have been using some of my Purigen bags for 6 months plus. When I regenerate, the Purigen returns to the original color and looks brand new. Is there a point when it is no longer functioning as it should. If so, is there some condition I should watch for, discoloration, smell???

I do 50% water changes weekly, clean my XP3 and rotate the Purigen every 4 weeks. Aquarium water looks and smells great so I assume it is still filtering properly. I use Seachem prime for the water changes so I don't have to worry about my water conditioner fouling it.

I have looked at the Sechem literature and searched a couple forums. I believe it was on here that someone mentioned they dispose of it after "X" number of regeneration cycles.

It is so expensive and I am getting ready to set-up another tank so I don't want to be wasteful but want to make sure it is still working properly.

Any thoughts?

Mike