The normal cartridges for the 350 are essentially filter pads with a bit of charcoal. These empty shell cartridges all you to customize to your filter's needs. You can use filter pads, floss, ceramic rings, charcoal, purigen, etc. One note--it's not immediately obvious from the picture, but the interior is not completely hollow. Rather, there are rows. So when you fill these, you'll have to work in strips. Not a huge deal to me.
Never received my order or refund no e mail on when u might ship very disappointing not pleased at all
Very happy 5/8/2013
I am very happy with my purchase. the price is great and it was delivered on time and it saves me money. Great product and support. Thanks.