Tetra FF FilterFloss The advanced Tetra FF fine filter fleece has been specially developed for the Tetra external filters. The Tetra FF fine filter fleece reliably removes the finest particles and should be used as the last filter material. Please rinse in warm water before use. The filter fleece should be replaced regularly (all 4-8 weeks) to ensure optimal filtering. All Tetra filter materials help maintain healthy and clear aquarium water. - Tetra FF filter fleece: for the Tetra EX external filter 600 Plus and EX 800 Plus and an aquarium size of 60 to 300 litres. - Tetra FF filter fleece: for the Tetra EX external filter 1200 Plus and an aquarium size of 200 to 500 litres.