Rainsoft Gold Series

I have a Rainsoft Gold Series system installed in my home. The main system has two cylindrical tanks and a salt tank. I'm curious what each of the two cylindrical tanks do. From the research I've done, one of them might be filled with with some filtration media.

Here are the model numbers of our equipment:

Tank 1 (Computer mounted on top): EC4 100 CV 110V PT
Tank 2: QRS 1044 SH
Ultrefiner RO System: 21179

I'm asking because the alarm is going off and I simply can't justify paying someone $100 just to show up, press a button and swap out filters that I'm perfectly capable of doing myself. I know how to reset the system via the service menus, so that isn't a problem. We've had the system for 3 years and the only filter I've replaced is the center cylinder on the RO system. So, here are my questions:

1) On the RO system - what besides the center cylinder would ever need to be replaced and when? Do all 3 of the cylinders on the RO system need maintenance?

2) What, if anything, needs to be replaced on the 2 tank softener system as a part of regular maintenance and when? If so, is this something only Rainsoft can do, or is it something a capable homeowner could accomplish?