Biological Filter foam for TetraTec EX600/700 and other external filters. Efficient biological and mechanical filtration. – High surface area to support growth of beneficial bacteria. – Reliably removes medium sized particles from aquarium water. Rinse in lukewarm water prior to use. Clean as necessary in a bowl of aquarium water. To maintain biological activity do not wash under tap water. Suitable for most external filters (ensure foams fit neatly into media basket).