Filtration medium

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(57) Abstract : A filtration medium comprises a first grade of glass particles and a material suitable to form a water permeable re- tention layer. Preferably, the filtration medium comprises at least two grades of glass particles. The first grade is preferably dis- tributed substantially over the range of 0.75mm to 1.7mm. The second grade is preferably substantially in the range of 1.7mm to 3mm. In a further aspect, a filter is described having a water permeable retention layer supporting a filtration medium substantially comprising the first grade of particles. The retention layer may comprise the second grade of glass.