Flush RO twice per week from your source tap and disconnect your DI before doing so.
PS
Just found out this week that resin goes off, it may have been mentioned on here before and i missed it, but i got a high reading last week, changed resin, and still a high reading, so ordered 3 prefilters, changed them, still a high reading, and after enquiring about this, the suppliers reckon after 6 months of keeping resin, even in a selaed container it can go off.
Ordered small 10" canister with fresh resin in, and TDS back down to 000, mind the old prefilters which have been in 6 months were black.
Hope its a help