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TDS changes before DI


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  1. #1
    XSiVE - Reefkeeper
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    Default TDS changes before DI

    this seems odd, I just got a dual inline TDS meter and of course Im playing with it... I have my RODI set up into my ATO bucket with a float valve... when the float valve closes, the back pressure causes the auto-shutoff valve to turn the RO off.. typical configuration.

    In normal running situations Im getting 5TDS out of my RO, but here's where I think it's a little strange. When the autoshutoff shuts the system down, the TDS starts creeping upward to around 100. once the system starts flowing again that number goes back down to 5 eventually.

    Im really not sure what this could be from, unless the DI resin is leeching its leftovers back ward as the water sits there not flowing.

    any ideas?

  2. #2
    AZDesertRat - Reefkeeper
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    Quote Originally Posted by XSiVE View Post
    this seems odd, I just got a dual inline TDS meter and of course Im playing with it... I have my RODI set up into my ATO bucket with a float valve... when the float valve closes, the back pressure causes the auto-shutoff valve to turn the RO off.. typical configuration.

    In normal running situations Im getting 5TDS out of my RO, but here's where I think it's a little strange. When the autoshutoff shuts the system down, the TDS starts creeping upward to around 100. once the system starts flowing again that number goes back down to 5 eventually.

    Im really not sure what this could be from, unless the DI resin is leeching its leftovers back ward as the water sits there not flowing.

    any ideas?
    What you are seeing is TDS creep. When the ASOV starts to close it places backpressure on the treated water side of the membrane causing the water to osmose or equalize on both sides of the membrane. Since RO water has fewer ions and is considered agressive it attracts the untreated water right through the membrane fabric, or osmosis.
    Once the system starts again it takes a few minutes for the TDS creep to flush itself out and the treated TDS to drop back to the normal 96-98% rejection rate if its in good shape.

    One big reason I do not recommend float valves is in normal operation they start and stop frequently since they have such a narrow operating range compared to two float switches set a disatnce apart. With float switches you don't necessarily eliminat TDS creep but you reduce its frequency dramatically so the effects are minimized and DI resin lasts much longer.

    One thing you can do to reduce the effects, if you have sufficient ATO storage capacity, is shut the RO/DI unit off manually after the ATO reservoir is full and allow it to drop some distance before turning the water supply or ball valve back on again so it cycles less often.

  3. #3
    XSiVE - Reefkeeper
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    Default

    I was afraid you were going to say that about shutting off the ro.

    I've got it going to a 32 gallon brute so I definitely have the capacity, the issue is remembering to turn it off or more likely back on again..

    Thanks a ton for the explanation

  4. #4
    AZDesertRat - Reefkeeper
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    Quote Originally Posted by XSiVE View Post
    I was afraid you were going to say that about shutting off the ro.

    I've got it going to a 32 gallon brute so I definitely have the capacity, the issue is remembering to turn it off or more likely back on again..

    Thanks a ton for the explanation
    Remembering can be tough when you get my age!
    I use two float switches and a solenoid valve set 12" apart which for me equates to 11 gallons in my 23G Rubbermaid recycling can. I go 2 to 3 days before it kicks on again

  5. #5
    XSiVE - Reefkeeper
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    Default

    Perhaps this constant on/off and the resulting TDS creep is why Im eating through DI resin so quickly too... (besides the idiotic accidental reversal of 1 and 5 micron carbon blocks 6 months ago or so)

    hmm.. this float switch thing sounds similar to my DIY ATO except wired differently.. or with a different relay..

    im racking my brain on how the switches would have to be done, or which kind of relay used to make this work... Do you mind sharing the parts you used to put it together, or a source for a completed setup?

    Thanks

  6. #6
    AZDesertRat - Reefkeeper
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    Quote Originally Posted by XSiVE View Post
    Perhaps this constant on/off and the resulting TDS creep is why Im eating through DI resin so quickly too... (besides the idiotic accidental reversal of 1 and 5 micron carbon blocks 6 months ago or so)

    hmm.. this float switch thing sounds similar to my DIY ATO except wired differently.. or with a different relay..

    im racking my brain on how the switches would have to be done, or which kind of relay used to make this work... Do you mind sharing the parts you used to put it together, or a source for a completed setup?

    Thanks
    This is what I use:
    Solenoid Valve Controller by SpectraPure

    You could DIY it for a little less I would imagine but I got mine on sale.

    You really do not want or need two carbon blocks if you use high quality filters. You will get much more useful life and better membrane protection out of a single 0.5 micron absolute rated sediment filter and a single 0.5 micron 20,000 gallon carbon block then use that extra empty canister as another 10" vertical refillable DI filter. Note long time companies like Spectrapure, Buckeye Field Supply and PurelyH2o only use a single carbon. Two carbons goes back decades whe ncarbon technology was not as advanced as today. $5 in parts and 10 minutes will replumb the empty cartridge to a dual DI along with your existing one for longer DI life and better water.

  7. #7
    XSiVE - Reefkeeper
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    Wow thanks so much for all the help! Now I have a bit more to think about.

  8. #8
    NaplesAquatics - Reefkeeper CR Member
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    Quote Originally Posted by XSiVE View Post
    Wow thanks so much for all the help! Now I have a bit more to think about.
    I DIY'd mine for about a quarter the price of the Spectrapure unit. Then I spent another quarter of the price fixing my DIY. Then lost about three times the price of the Spectrapure unit in corals and fish when my DIY failed. Just warning you now...

    Spectrapure has some decent sales. There are others as well, but a fully engineered, working solution from the start is often the cheap way to go in reefing. Wish I'd learn that someday...

    Jeff

  9. #9
    XSiVE - Reefkeeper
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    Quote Originally Posted by NaplesAquatics View Post
    I DIY'd mine for about a quarter the price of the Spectrapure unit. Then I spent another quarter of the price fixing my DIY. Then lost about three times the price of the Spectrapure unit in corals and fish when my DIY failed. Just warning you now...

    Spectrapure has some decent sales. There are others as well, but a fully engineered, working solution from the start is often the cheap way to go in reefing. Wish I'd learn that someday...

    Jeff
    LOL I know how that goes, I've had my share of DIY mistakes but i cant get out of the mindset.. I think my options are either to buy something like linked above, or just deal with replacing DI resin a little more frequently and leave the float valve in place.. I may end up buying that once I go through the majority of the 7.5lbs of DI resin I currently have.

  10. #10
    AZDesertRat - Reefkeeper
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    In all honesty, I have not used but 4 DI cartridges in the last 3 years, At 20 oz apiece thats 5 lbs in 3 years. My DI resin lasts so long I cannot buy it in bulk as the shelf life of bulk resin under perfect conditions is only 6 months and one cartridge lasts me a year. You cannot DIY something like that.

    Back when I had a Watts Premier then later a Typhoon III I could use bulk because it only lasted 150 gallons no matter what I tried.

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