Marineland Bonded Filter Sleeve for Magnum 350 Canister Filter - 12 Total (4 Packs with 3 Sleeves per Pack) 12 Sleeves Total (4 Packs with 3 Sleeves per Pack) Marineland Bonded Filter Sleeve for Magnum 350 Canister Filter For the Magnum and HOT Magnum canisters For best result rinse and replace sleeve monthly. Specially designed to prolong the life of filter media by reducing the accumulation of waste and dirt particles.