What I wonder about is, pumice or Matrix has small pores. After awhile, it appears to me that the pores are all covered with bio film. Doesn't that nullify the effectiveness of the pores? I could imagine that Matrix is effective when new and clean. But, what about 3 months from now? In three months, wouldn't sponges, lava rock, plastic hair curlers be just as effective?
Seachem claims it does not need to be replaced because the pores are naturally too small for organics to clog, but large enough to be washed to have the old bacteria remains removed. I think it can be rinsed and boiled (several times) to be rendered reusable. I would just avoid the use of any products because of the highly porous nature of pumice stone.