Ok. I have now built the system and it works. Parts list ended up being: 3 x filter housings - clear plastic @$26 = S$78 1 x 5 micron sedminet filter cartridge (came with the housings) 1 x Granular Activated Carbon cartridge S$21 1 x 3.5 litre bag of mixed bed Di resin S$45 (enough for 3 fills, so that means S$15 per fill) Output speedfit elbow: S$3.80 Input hose connector: S$1.20 Total price is S$119, including first fill of DI resin.