RODI unit putting out 2ppm TDS?

Glad you got it figured out.

I use the BRS color-changing DI resin and that is very handy. +1 on double-DI canister, because when your DI resin starts to get close to being used up, your TDS will creep up as the contact time with the unsaturated resin decreases, and you end up having to waste 25-35% of your resin. I'm going to be getting another one pretty soon here myself because I'm at about 50%.

Good tip on replacing the #1 stage, mine here in WDM turns a nice brown color after about 6 months of on/off use.

+1 on cleaning, testing, and calibrating TDS meters. Although I'm not sure how much good that really does in some cases, I have a Hanna combo meter and one thing I've noticed is that when you put it in the calibration solution and it says it's done, the TDS is bouncing all over the place, and simply swirling the meter in the solution causes it to rapidly change, then you stop moving it and it goes the other direction, and I'm talking 20-40 points in each direction. I've never really searched to see if this is normal.

+1 on clean container. When I test, I put the container in the stream and let it fill up and dump it a few times, then swirl the meter in there and let it 'pump and dump' for a while, occasionally dumping most of the water out and letting it fill back up. I can watch the TDS drop right down to zero.

 

Just to be clear, we're looking at the #1 stage on the right (not left, duh) of those 3, correct? That is pretty gunky, close to what mine looks like and I consider mine due for replacement.
Also, when you say you are feeding a DI reservoir, expand on this.
One thing that happens with RO systems when connected to holding tanks is that you will get a TDS creep. I spoke to a guy who has 20+ years of RO unit experience once at length about this. When you put backpressure on a RO membrane, it allows a higher TDS on the effluent side to build up. You can see this for yourself for instance if you start with an empty holding tank and measure the TDS out of your RO, which should be low. Then let it fill all the way and leave it alone for a day, then test the TDS right out of the membrane and it will be very high. The low flow across the membrane (low pressure differential) allows migration of more of what can get through the membrane per unit of effluent (per gallon, per cup, etc) versus a lower amount that gets through under normal conditions (high pressure differential) per unit effluent. Essentially you are concentrating the TDS. As you build up the pressure in the DI holding tank, the TDS that you're feeding to the DI section gets higher and higher. When you drain your DI holding tank completely and start it flowing again, you hit the DI with a high TDS, unless you install a bypass valve between the two and let it flow free for a few minutes.
I have mine set up with a series of shutoff valves and taps so that when I make water, I can let the RO effluent flow free and clear the housing of stagnant water. I usually let about 0.5 to 1.0 gallon of RO go down the drain, then I close that valve and open the DI feed valve and let that run for a few minutes and then it's good.

 

Oh, I see, so neither is a pressurized storage container then? So RO/DI water in a Brute can, and RO up above, what's the RO above for? Just curious...

 

yes, checking TDS in the DT will tell you nothing really.