Ok, so I know there are people who are big supporters of this product and they will not appreciate any negative reviews of it. (I used to be one of them). But I have  to give an honest review so please hear me out.  Two of my tanks crashed after using regenerated Seachem. I am not saying this product itself caused it - I believe the use of BLEACH in the process of regeneration caused it. I followed the directions to use bleach to regenerate. I even doubled the Prime to neutralize the bleach after regenerating.

Everything was going fine (my tanks had been cycled for years) then one day my tanks crashed. The only change was that I had started using regenerated Purigen. Ammonia and nitrites were reading at the highest level on the chart. The beneficial bacteria was gone. Some of my fish died, some got ich and some got fin rot. So I'm just saying be careful using BLEACH on anything you plan on putting in your aquarium if your aquarium is cycled. It has taken me a month to get the ammonia and nitrites back to zero. I treated the ich using medicines and am still giving some fish antibiotics to treat the severe fin rot.

For me any benefits do not outweigh the risks and I am not using Purigen again. I will keep my tanks cycled to control ammonia and use floss to keep the water polished.

If you are going to use this, be very careful using the regeneration process. Using strips to test for chlorine on the purigen before putting it in the filter would be a good idea. Or use the product once then toss it. I am just sharing my experience.

UPdate 1-1-14: My tanks have been stable, everything within parameters, since I quit using this product. No crashes, no ammonia or nitrite spikes.
Ok, so I know there are people who are big supporters of this product and they will not appreciate any negative reviews of it. (I used to be one of them). But I have  to give an honest review so please hear me out. Two of my tanks crashed after using regenerated Seachem. I am not saying this product itself caused it - I believe the use of BLEACH in the process of regeneration caused it. I followed the directions to use bleach to regenerate. I even doubled the Prime to neutralize the bleach after regenerating. Everything was going fine (my tanks had been cycled for years) then one day my tanks crashed. The only change was that I had started using regenerated Purigen. Ammonia and nitrites were reading at the highest level on the chart. The beneficial bacteria was gone. Some of my fish died, some got ich and some got fin rot. So I'm just saying be careful using BLEACH on anything you plan on putting in your aquarium if your aquarium is cycled. It has taken me a month to get the ammonia and nitrites back to zero. I treated the ich using medicines and am still giving some fish antibiotics to treat the severe fin rot. For me any benefits do not outweigh the risks and I am not using Purigen again. I will keep my tanks cycled to control ammonia and use floss to keep the water polished. If you are going to use this, be very careful using the regeneration process. Using strips to test for chlorine on the purigen before putting it in the filter would be a good idea. Or use the product once then toss it. I am just sharing my experience. UPdate 1-1-14: My tanks have been stable, everything within parameters, since I quit using this product. No crashes, no ammonia or nitrite spikes.