The membrane may not be properly functioning which is causing the DI
resin to deal with greater TDS
content which in turn accelerates resin exhaustion. (the RO
membrane should be the work horse of the system, not the DI
membrane should be removing 95%+ (ideally 98-99%) of the TDS
from the source water. Please post your faucet water TDS
and RO TDS
Did your RO
output ever register a 0ppm?
I usually change out the DI
resin when RO
increases to 3-5ppm (and that's after many months of 0ppm RO
You may need to get some new DI
resin (after you solve your potential RO
membrane problem), if the RO
output is already at 6ppm..