Koi Pond Filter Media » Alphagrog

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 ...

Alphagrog is made of a highly porous material that contains many thousands of tiny pockets in which bacteria can thrive making in an ideal material for biological filters

Its only draw back - sharp on the hands when cleaning ... so please wear gloves..