I have installed 3 whole house water filters and am confused about
this question.

The first filter is the cheap rust and big stuff 20 micron filter.

The second filter is the 5 micron charcoal taste and odor filter.

The 3 rd filter is the very expensive 1 micron filter, which I can't
afford to buy, so I need your opinion.

Do I leave the 3rd filter empty or do I put two of the cheaper 5
micron filters in the 2nd and 3rd positions?

DK