I use a 5 stage RO/DI setup for my water making with a sediment filter, 2 carbon blocks, a mixed bed resin filter and the RO membrane. I have been runing for about 6 months and I am kinda surprised I am not seeing anything dirtying up my sediment filter or any color change from my resin filter. I check the TDS level every week when I am making a bunch of water and it is always 0. What should I expect on time for these filters and what is your experience? Am I missing something that TDS doesn't pick up?