Fluval SPEC/EVO/FLEX Foam Filter Block. The SPEC / EVO/ FLEX Foam Filter Block provides effective mechanical filtration by trapping large particles and debris. Key Features : Specifically designed for the Fluval Spec, Evo and Flex desktop aquarium series Equipped with convenient handle for easy handling Foam Filter Block is suitable for: EVO 13.5 G (52 L) SPEC 2.6 G (10 L) SPEC 5 G (19 L) EVO 5 G (19 L) FLEX 9G (34 L)