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RO unit and DI resin quesiton

Discussion in 'General Discussion' started by Jamie, May 19, 2013.

  1. Jamie

    Jamie Well-Known ReefKeeper Vendor

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    So I have had a RO/DI unit for a long time and my incoming water only has about a 170ppm TDS. After the RO alone I get 0 TDS then it is ran through the DI resin and comes out 0 as well. My question is, why does my resin get used up over time until it is exhausted if there is 0 TDS going into it to begin with? I've always scratched my head to this but never really though much about it. Anyone know?
     
  2. Deleted member 1172

    Deleted member 1172 Guest

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    What kind of resin do you use? I've heard BRS resin turns brown well before tds creeps up! I think its more oxidation than anything, which would make sense to me.
     
  3. Jamie

    Jamie Well-Known ReefKeeper Vendor

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    Yes it's the BRS color change nuclear grade resin but the TDS is already 0 into the resin yet it still changes color. I've read that DI resin absorbs Co2 but does not measure on a TDS meter, could this be what is causing the color change of the resin but 0 on the TDS meter?
     
  4. Big John

    Big John Inactive User

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    I'll follow this one, I've often wondered the very same thing.
     
  5. Roman Experienced Reefkeeper

    Cedar Rapids, IA
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    I.have never had a membrane register at zero. Even a brand new one.I didn't think they have a 100% rate. I think I have read that they have a 97% rejecting range.Which is why you use di resin to get to zero. Maybe guage is off slightly.
     
  6. Tickyty

    Tickyty Well-Known ReefKeeper

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    The lowest reading I am getting out of my membrane is around .01/.02 area. This is a good question for BRS however. Have you contacted them to see what their suggestion is. Probably not a bad idea to hang on to the resin until the TDS starts to rise.
     
  7. Tickyty

    Tickyty Well-Known ReefKeeper

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    Well I had to go out and ask BRS and this is what I was told.

    On a technical level, half of the DI resin has a pH indicating dye inside of it. As the ions exchange, the pH in the dye changes causing that half of the resin to turn from blue to clear. Because the other resin is brown, it gives the appearence of turning from blue to brown. It's possible for the pH of the water to be such that the color can change without being depleted, but its pretty rare. Most likely circumstance if your cartridge has turned entirely brown is that your getting close to the end.

    I then asked: So the color change is just a barometer of the depletion and as long as I am monitoring the TDS then I should be good until they start to rise?

    Response: Correct, its the TDS meter that has the ultimate say, but a good bet you want to atleast get an order in for some resin as your likely to need it sooner rather then later


    I would have resin on hand and wait for the TDS to begin to rise. I have a Dual DI system so I will just start waiting until the second canister is about 20% depleted before I change. I guess that is one of the drawbacks of having 2 chambers.
     
  8. Jamie

    Jamie Well-Known ReefKeeper Vendor

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    MY TDS meter does not go below 1 so maybe it's just not picking up the small amount of TDS before the DI resin either. I just change it when both canisters change color.
     
  9. Tickyty

    Tickyty Well-Known ReefKeeper

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    Which TDS monitor are you using? I am a little confused here. If your meter does not read below 1 how do you know that it is 0 when it leave the RO membrane? Seems to me that there may be an accuracy issue with your meter.
     
  10. Jamie

    Jamie Well-Known ReefKeeper Vendor

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    I have the in-line DM-1 Dual In-line TDS that BRS sells. After ro 0 and after DI 0 are my readings. If I put it in my tap water I get around 170ppm on it. It reads in single digits from 0 to 999ppm theres no decimal on the display. Didn't know that any were that precise.
     

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