You said your RO
You've got an RO
membrane in one canister, and DI
resin in the last canister in the system. Which is it that is turning colors?
If it's your DI
cartridge that is turning from green to brown, that normally means your DI
resin is shot. As CaptainAhab mentioned, how long the DI
resin lasts will depend on the TDS
of your source water. With really high TDS
, you might blow through the resin that fast if your RO
membrane is only, say, taking out 95% of the junk. But with low TDS
(say less than 100), I'd expect it to last longer than that.
But yeah... if the output is at zero, you're still OK. Even after the color changes, there's still a fair amount of life in them.