Thanks Josh for your input.
I Had not changed my Carbon filter till last week. Someone had told me when I bought it that it didn't need to be changed very often, I should have done some more checking. Any way, the pressure over time had dropped and I figured it was the carbon, but after I changed it the next job my TDS was crazy high. I freaked out! Had two houses that day.... did it with 11-15 tds. We had to redo a few panes by hand but no big deal. Then I got home did some checking and ordered a new R/O (4x40) I didn't order it from here so I won't say where, however I got it for $277 free ship. Cheapest I ever saw.
Then I remembered I had an extra D/I ready to go in my office. BAM! That solved it! Next job my TDS was 000 coming out! Whew...
But now I have this R/O coming and not sure if I need it yet. I heard they must be refrigerated so I guess I'll stick it in my extra one in the garage.
Back to this, so, you change the carbon every six weeks? That is not cheap, my carbon/KDF cost my like $70. I might as well wait till my R/O goes out at that price. My filters are 4.5x10. Maybe I need to do some more checking and see if I even need the KDF in there. That is the only filter I don't even know what it is for and really raises that cost of the carbon.