Alfagrog is a Volcanic rock and has been used now for several years with a great deal of success. It is very inert and soon colonises with beneficial bacteria. It's high surface area makes it an ideal material on which micro organisms can adhere and boost biological decomposition of pollutants. The highly porous material contains many thousands of tiny pockets in which bacteria can thrive making in an ideal material for biological filters.
Alfagrog is a porous ceramic pond filter media which is made under controlled conditions in Staffordshire, U.K.
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