I have recently updated the Foz Down web page with the stores that carry it for sale. Here is the updated page.
http://www.oceanfreshaquarium.com/foz-down.html
For people in the Langley, Abbotsford, Chilliwack, Hope area you can purchase directly. If there is no local store to you I believe Eli(Fiji Reef Rock) ships as well as myself.
I have seen clam filters successfully used. The 150 gallon system had over 50 large clams and a ton of fish with no algae problems.