Yes in Mesa our tds comes out at 1100 to 1200, it is awful. I will most likely be installing a pre filter in the next week.
I used to live 20 miles away in South Phoenix and there our tds was 700 to 800. I have heard that the water in some areas of Tempe is around 2000.
This is another reason I bought the system I did, I need a much help as I can get lol
Do you have a whole house filter? I would recommend adding that instead of just an additional prefilter