Looking at how the membranes work on an RO, if you have a 300GPD system surely the last membrane in line gets all the really bad water and therefore would be the first to stop working.
So, in mind that suggestions are that your membranes should be changed every one or two years, do you think it would be a good idea to change the last membrane when you put new sediment/carbon filter in and then rotate the membrane so the new one becomes the first, first becomes second and second becomes the last one?
Or is it way too much messing about and not much of a gain over changing them once a year?