A filtration system includes an outer casing (210) that houses a plurality of elongated inner casings (220A-220F), which in turn house a plurality of filtration membranes. The outer casing, inner casing, and filtration membranes are disposed relative to one another to provide a three-flow channel system that provides additional feed fluid at one or more membrane couplings between membranes of the same inner casing. Ths arrangement defines a feed fluid flow path in which a feed fluid exiting from an upstream filter into a downstream filter is diluted by additional feed fluid.