EHEIM Substrat Pro Biological Filter Media (Sintered Pearl-Shaped Glass) 2L Made of highly porous artifiical sintered glass material Unbeatable surface area structure of 1800 sq ft per gallon Can be reused by lightly rinsing with aquarium water every 1 to 3 months and replaced every 3 to 6 months Provides longer intervals between required maintenance For use in all EHEIM filters (Classic, Ecco, Pro 3, Pro 3e)