A solid natural stone which contains many pores, cavities and channels. Zeolith works in an adsorptive manner, i.e. environmental toxins and decayed products are directly attracted and retained by the system of cavities through strong electro-static fields. Zeolith encourages the formation of natural bacteria and Microbes and acts as an ion-exchanger and catalytic converter. A very practical reccomandation is to put the filter material in the HOBBY Net filter bag.