I use lava rock they do a great job. I put them in a laundry bag so thy
are easy to take out of veggie filter when its time to clean. My pond
was clear and its 4' deep I could see all the way to the bottom. The
water did go green when I first set up the pond but it cleared up in
about 3 weeks and never went back green.


http://community.webtv.net/rebeljoe/POND