RO/DI part questions

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I have a spectrapure 60 GPD unit (http://www.spectrapure.com/St_osmo_p2.htm), and i just started getting a reading of 2-3 tds yesterday so i am assuming this means i am ready for a change in filter components.

How do i know which parts i will need?

Do i need:

The sediment filter?
http://www.spectrapure.com/St_replac_p1.htm#tec

Carbon block?
http://www.spectrapure.com/St_replac_p2.htm#carb

DI replacement cartridge?
http://www.spectrapure.com/St_replac_p4.htm#mix

RO membrane?
http://www.spectrapure.com/St_replac_p3.htm#spec

Membrane flow restricors?
http://www.spectrapure.com/St_replac_p3.htm#flow

I really dont know which parts should be replaced (all of them?), and any help in this would be appreciated!