The pumice used to create this fountain is a natural biological filter in itself. As the water runs over the volcanic rock it filters it. Just do a water change one time each month.
This particular bowl was a one-of-a-kind ceramic bowl. So it is not available. The bowls available are resin. They are 12″ diameter and have a simulated stone finish to blend with the pumice stone. Click here http://www.youtube.com/watch?v=zVk8H4aSDhE&feature=youtu.be to see a YouTube video.