RODI not doing what it's supposed to!

[hillegom]

Originally Posted by 11purewater

The DI is there to filter the Ro product water to 0 TDS(non conductive) if you can't achieve it with the RO membrane alone.For example 200 TDS feed water going through a membrane @ 98% rejection=4PPM product water,DI after brings it to Zero.

I agree. The DI is the most expensive, and it should be last. You try to get the lowest TDS out of your system that you can and then send it to the DI where it will come out at 0 TDS.
If after the DI, it is not 0 then the DI is exhausted and you need to replace it.