Matts right, but you could buy the 10 inch cannister from Purefreedom for a tenner which is full of resin.
When i started i got a load of resin and 6 months down the line when reading was higher on TDS i changed it and all the resin had gone off, so bought a cannister for £10............................................... Thats if they remember to send you it!

My set up on pipes is
Red ......waste
Blue......RO to DI
White.....Pure water
Not that it matters which colours you use as long as youve got them in right place!