Hi,
We have an RO system and polish of with a DI unit on the van. Our pre DI figure from the RO is always about 14, polished up to 000 by the DI Unit.
Last week we noticed that despite the water still going in at 14 the after DI figure was slowly failing to polish to 000.
Went from 000 to 002 then 003, 005. Resin changed and back to 000.
I read somewhere you can still produce good results with water not polished to 000 but dont know when it becomes unefficient.
Hope this helps a little but others will be better informed on this subject.
Sarah