TDS and replacing DI resin...

[afboundguy]

It's probably been about 1.5+ years since I've replaced my DI resin, prefilter and a carbon block and I flushed the unit and noticed my TDS actually went up. It was 1 (which prompted me to order new DI resin) but now it's at 4. Does it take a bit before it gets back to zero? I can't remember how long it should take...

 

[this is me]

What are you flushing? The RO filter or the whole unit? You can only flush the RO to make it work better(if not fully exhausted). A DI that has 4TDS at the output will NEVER be lower than that regardless how long you running it.
Yes, there’s a residual high TDS water coming out of the DI after it has been sitting. But as soon as you send water into the DI and that residual water has flowed out, the TDS on a good DI will be 0.

 

[Greg Hiller]

Also note that that TDS reading of zero will ONLY be on water just as it is exiting the DI unit. Once the water sits around for a short period of time it will pick up CO2 from the air, forming a small amount of carbonic acid and the TDS will rise slightly before it stabilizes once it's in equilibrium with the level of carbon dioxide in the environment (scarily higher every year BTW). https://www.esrl.noaa.gov/gmd/ccgg/trends/