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Thread: RO/DI system question

  1. #21
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    I can attest to at least the fact that the stagnant DI water is above zero. not 1330, but definitely not zero. Actually I haven't tested the stuff right out of the DI in a while, I usually let it run for 30 seconds before even bothering. Next time, I will test it!

  2. #22
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    Quote Originally Posted by kerry View Post
    I have a question about DI filter replacement. At what PPM do you guys change the DI filter media? Mine has just started to read 1-2PPM TDS. I am only using it for top off as you all now I have scrubbers so I dont water change. My tanks (all three) usually need about 4-6 gallons per week for Kalk top off. Is 1-2 PPM TDS bad enough to change the DI media?
    I would suggest reading this. It contains everything you will need to know;
    http://reefkeeping.com/issues/2005-05/rhf/index.php

  3. #23
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    Good stuff in that link.

    Several issues arise relating to the depletion of the DI resins that aquarists need to be aware of. Primary among these is that when a DI resin becomes depleted, that does not simply mean that the water passes through just as it came from the RO effluent. It may actually be much worse from an aquarist’s perspective. The reason for this is that while the DI resin is functioning properly, all ions will be caught. But when it is depleted, not only the new ions are coming through and might show up in the product water, but so are all the ions that ever got into the DI resin in the first place. The total concentration of ions coming out of the exhausted DI resin will not be raised as compared to the RO's effluent, but which ions are released may be very different.

    In the DI descriptions above, I did not address the fact that some ions will show a greater preference for attachment to the resin than will others. When the resins are not depleted, it does not matter what the ions’ affinity is, as all are bound. But in a depleted scenario, when there are more ions than ion binding sites, those with a higher affinity for the resin will be retained, and those with a lower affinity will be released. It turns out that silicate is found at the lower end of affinity for anion resins. Consequently, if the DI resin has been collecting silicate for a long period and is then depleted, a large burst of silicate may be released.

    Perhaps even more of a concern is ammonia. In a system with chloramine in the tap water, the DI resin will serve the important function of removing much of the ammonia produced by the chloramine breakdown. Ammonia has a poorer affinity for many cation-binding resins than do many other cations (e.g., calcium or magnesium). Consequently, when the DI resin first becomes depleted, a big release of ammonia from and through the DI resin is likely. I recently had a DI resin become depleted, and the effluent contained so much ammonia that I could easily smell it.

    Other complications can also impact resin depletion. One potentially important issue is that the anion and cation-binding sites may not become depleted at the same time. Figure 10 shows this scenario when both types become depleted together, with sodium and chloride in the effluent. But, it is possible for one to become depleted first, and in that case, the pH of the effluent can swing far from neutral. Figures 11 and 12 show what happens when a lot of carbon dioxide is present, as is the case with some well waters. Initially, it is mostly bound as bicarbonate, and the effluent is essentially pure water. Note, however, that as the bicarbonate is removed, the anion binding resin is being taken up with bicarbonate, while the cation-binding resin is unchanged and is therefore not being depleted.

  4. #24
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    Quote Originally Posted by Ace25 View Post
    Good stuff in that link.
    He certainly knows his stuff. You never want to process water through a spent system. And due to the instablility of pure water, testing is fraught with variables. However, the science proves the technology. Hats off to Randy.

  5. #25

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    since we are on the RO/DI thread, I recently replaced all my filters and membranes on my system when I moved to the new house. my set up is a follows Sediment>Carbon>Carbon>RO>DI>DI. My tap water is around 400 TDS according to my hand held digital meter. Coming out of the RO, TDS is about 6. After the DI stage, upon start up it is 19 but after running for a few minutes it goes down to 9. I made 130 gallon of water and the TDS still reads 9. What am I doing wrong?

  6. #26
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    Not sure? I run mine just like that but only one DI unit. My tap is 30-70 TDS at any given test. After the RO its about 4 TDS average even after a year and now the DI is showing 1 TDS after a year.
    150G. Reef/Mix
    125G. 3 Regular Oscars/1 Jack Dempsey
    75G. 20+ Africans
    40G. Fish/Reef. Algae Scrubbers on ALL my SW
    10G. SW Fish/Reef.
    10G. SW Hospital/new fish quarantine/pod breeder tank
    6 stage RO/DI system 200 GPD.

  7. #27
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    Quote Originally Posted by akando View Post
    since we are on the RO/DI thread, I recently replaced all my filters and membranes on my system when I moved to the new house. my set up is a follows Sediment>Carbon>Carbon>RO>DI>DI. My tap water is around 400 TDS according to my hand held digital meter. Coming out of the RO, TDS is about 6. After the DI stage, upon start up it is 19 but after running for a few minutes it goes down to 9. I made 130 gallon of water and the TDS still reads 9. What am I doing wrong?
    Does your TDS meter read 0 when you dry it and expose it to air?

  8. #28

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    garf, yes it does.

  9. #29
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    Quote Originally Posted by akando View Post
    garf, yes it does.
    I assume that the D.I filters are not new ones.

    Are they full of water, without large air bubbles?
    Is the flow rate through the canister similar, or slower,than it was with the previous membrane?
    Are you sure the tubing etc, has been connected up correctly?
    Did you "Break in" your new membrane, to remove any preservatives to waste?
    Were you having TDS issues before you replaced your filters?

    It may seem tedious sending multiple posts, but you need to eradicate the simple faults that can appear before a "Replace your resin" quote is made.

  10. #30

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    The DI Filters are Brand New.The first one is full of water, the water flows into the second one but doesnt accumulate.

    Flow rate I am unsure about since I switched from a 150 GPD set up to a 90 GPD membrane.

    I am almost positive tubing is hooked up correctly. I put a 90 GPD restrictor in when I installed the new membrane. I payed attention to all the IN and OUT markings on the Canisters.

    I did "break in" the Membrane.

    I did not have a TDS meter at the previous house, I started to notice a pressure drop and had a little tax money left over so I decided to just change everything when I moved.

    Thanks for your help.

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