We carry a wide selection of biological and mechanical filter media, including filter pads, bulk filter media, K1 Kaldnes moving bed media, bio-balls, Matala sheets, activated carbon and more.
For more information on pond filtration see our Pond Filtration Basics page
You can use rainwater to fill your pond, but keep in mind that it is very soft water. If you primarily use rainwater, be sure to check your pH regularly because it could become too low and cause serous problems.