RODI water reading 3 TDS initially, but then goes back to 0???

mochaclownlover

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Pretty sure this is the right area to post this. So I just replaced the three filter canisters of my 4 stage RODI unit. When I go to make water, it comes out registering at 3tds, then after about 2-3 mins, it goes back to 0. I bought some other tds meters to check the water with and they are reading back the same. I packed all the di resin very well initially and also checked for channeling after I realized there was an issue. I also just replaced the ro membrane less than 6 months ago, so I don’t think that would be it. The only slightly different thing is the psi is usually at 60, but it is currently reading 59. I’m honestly stumped on this and any thoughts on this would be greatly appreciated.
 

ScottR

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It’s very typical for the water to read over zero when you first turn it on. I guess it’s flushing water that was sitting stagnant. Then as fresh water gets through, it will read zero. Mine typically will read 1-2 initially for maybe 30 seconds then will become zero.
 

Vwluv10338

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Do you have DI? It takes a few minutes for the membrane to work well. I have turned mine on and seen the TDS drop from 50 to 13 at the membrane but my DI takes it to 0. My membrane is about due for a change.
 

ScottR

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@ScottR That's what I had initially though, but I ran the unit ~2hrs just running and letting the water drain down the sink. Maybe I didn't flush the unit long enough during that initial process?
So it ran at 3 TDS for 2 hours? That’s a bit odd
 

Twoddler

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@ScottR That's what I had initially though, but I ran the unit ~2hrs just running and letting the water drain down the sink. Maybe I didn't flush the unit long enough during that initial process?
I think I ran off about an hour, when I changed filters and resin, water pressure does have an effect , but 1 psi not to sure
 

Shirak

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@Twoddler, does your unit always start at 3tds or does it just happen after you change the filter/media?

It's called tds creep. When the unit sits idle the TDS between the waste side and the RO side of the membrane will equilibrate slowly. I have a bypass valve between the RO out and the DI in so I can flush the first quart of water into a container before sending it through the DI. It's good for the houseplants and espresso machine:) If I didn't I would be sending 140 TDS water through my DI for the first 15 seconds which would probably not get all the way down to 0 after the DI and it uses up the DI resin faster.
 

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