reply to hawk
i have been using ac 300 for just over 2 yrs, now. On one of the forums, it was suggested to use sponge on bottom, filter floss in middle, and sponge on top.......my water is crystal clear and has been ever since......i just rinse the sponges in a bucket, every 2 weeks and replace the filter floss, as it is so cheap.
As far as zeolite and carbon, i never use the stuff, (havent had a reason to, but do keep some on hand, just in case).....HTH