When to change DI when RO puts out 0 TDS

[Richard Hercher]

I purchased a 4 stage RO/DI last year in March that didn’t have color changing dye. I hooked up a Dual TDS meter’s first probe after my RO membrane and second after my DI canister. Before the DI canister, I have a valve to drain out the “TDS creep”. My routine is, I open the RO flush valve and the TDS Creep Valve, watch the TDS meter go from about 80 to about 15 (takes about a cup of RO product water, the rejection water goes right into the sink drain). Then I close the flush valve, watch the TDS meter jump from 15 to about 30, and wait until it goes down to about 3 or 4. Once it gets below 5, I open the valve to my DI resin, close the Creep Valve, and check that the second probe (the one measuring water coming out the DI canister) reads zero. A year later, it still reads zero out of the DI canister. According to the first TDS meter, after running the RO membrane for about 15 minutes, my post RO membrane TDS meter registers 0.

I worry that my old resin might be past it’s prime even though the readings say it’s no big deal. Should i wait until that first time the DI tds meter says 1, or just replace it because 11 months on one batch is a good run and i shouldn’t temp fate? I’ve already ordered a color changing resin, should be here Friday, but wondering if I’m being a chicken

 

[ironman187]

I wouldn't bother until you start seeing some TDS. BTW, I really like your methodology, it's a bit complex, but definitely saves your DI resin. I think I'll be buying some valves shortly.