I generally run 250ml of Purigen in my filter so had bought two bottles of it so I can easily replace during filter change and have next round recharged and ready. One bottle I put in Boyd's Chemi-Bags. While rinsing after 2nd recharge the bag tore. These are nice as they are $2.xx each but any tear in bag will send Purigen all over tank. Amazon.com : Boyd Enterprises ABE16720 2-Pack Chemi-Bags with Ties for Aquarium : Aquarium Filter Accessories : Pet Supplies The other bottle I had put in Seachem The Bag but don't have any idea on longevity as I JUST bagged it. I do think the cost is a bit much at $8.xx per. Amazon.com : Seachem The Bag Filter Media Bag : Aquarium Filter Accessories : Pet Supplies To be honest, if The Bag is best choice I am better buying 3 x 100ml pre-bagged Purigen for $8.xx each rather than saving by buying in bulk. Any alternates? Purigen is pretty small so not all bags contain it well.