I have been having problems with Phosphates in my tank and found out that my home RO still shows high Phosphates ( almost 5.0) I just got a new RO system that is 100gpd and installed it. I also just got a TDS meter. Before RO the meter says 1671. After RO it reads 167, and after the DI it reads 4. Everyone told me that after the DI filter is should be zero. Is this alright, or is my water so bad I need a second DI filter?