Looking for a refillable filter cartridge for 4×21" housings?_x000D_

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This is it._x000D_

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These refillable cartridges fit the 4×21" housings from many different manufacturers._x000D_

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Fill with our virgin bulk DI resin to save big on your filter cost._x000D_

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Holds 1/10 of a cubic foot of DI resin.