TDS in RO water

Discussion in 'Equipment' started by screebo, Nov 4, 2009.

  1. screebo

    screebo Supporting Member

    I'm wondering how your RO water pans out when you measure the TDS. I've not changed the membranes in my GE Merlin since I bought it about a year ago. I noticed that out of the spigot, it comes in at 10 PPM of disolved solids. Strangely enought, in the ATO reservoir that has only had RO water in it, the reading is 50 PPM. I attribute this to contamination somehow (not a biggie) as a by product of leaving about 1/3 of the water in the reservoir before I refill it. My water is typical Peninsula Hech Heche water.

    Question: how does your RO water measure up when you test TDS? At what point would you suggest changing out the membrane/s (mine runs two membranes and is an "on demand" system with no tank)
  2. tuberider

    tuberider Guest

    Depends on your pressure and incoming TDS, for a hobby/home unit 2-3ppm is pretty good. Considering where you're at you should be somewhere around there.

    Changing the membrane depends on how much water you use, and how often you change prefilters. When I start to see a rise in TDS (above 10ppm) I change membranes.
  3. screebo

    screebo Supporting Member

    That helps. Thanks.
  4. JAR

    JAR Supporting Member

    I have an R/O DI unit that is at 0 TDS when new with new DI resin. As the DI resin gets used up the TDS goes up. I have had the same membrane for 2 years and DI was new 8 months ago. Now at 4 TDS.
  5. GreshamH

    GreshamH Guest

    You must have a great water source then :)
  6. Tumbleweed

    Tumbleweed Guest

    I run an RO/DI that MELEV sells on his sight. I have 0TDS coming out of the end. It stays that way for about 8-9 months then starts to climb. I just replaced my pre filter set and DI filter after 15 months of use, and had a ready of 5 on my meter before I changed them.
  7. GreshamH

    GreshamH Guest

    If you have chloramine or chlorine in your water source you'd better change your carbon filter more then that, otherwise you are ruining the membrane.
  8. sfsuphysics

    sfsuphysics Supporting Member

    Depends how much water you're using as to when to replace the filters.

    IIRC the rejection rate of a standard RO membrane is somewhere in the ballpark of 96-98% so test your tap TDS, and your output TDS and that can let you know how closer that is. There was for the longest time the 100GPD membranes that apparently had rather low rejection rates (~90%) but it was a tradeoff people were willing to pay for faster production, not quite sure if that's still the case though.
  9. GreshamH

    GreshamH Guest

    Mine uses dual 100gph for that very reason.. still the case
  10. screebo

    screebo Supporting Member

    So at 10 ppm my livestock is living in sewer water! ;)
  11. tuberider

    tuberider Guest

    Better yet double them up and use a Pentek Chloramine reducing carbon filter as your second stage of carbon and change often :)
  12. VietNR1

    VietNR1 Guest

    Hey guys,

    A friend of mine just got into the hobby and I was tellin him about RO/DI units for water and he said that he use to have a DI unit when he washed cars for dealerships at night. By using the DI unit he would be able to wash cars and let them air dry and have no water spots. If we used the DI unit without RO would it be close if not the same?

  13. kvosstra

    kvosstra Guest

    There are commercial units that are simply DI beds - (see e.g. Culligan). The combination of RO and DI allows you to remove "all" contaminants from the water, as the DI alone will not remove all potential pathogens and contaminants in the water, since it only removes things that are ionically charged.

    DI is also somewhat expensive, so for reefers, the cheep RO/DI is a pretty good system.
  14. sfsuphysics

    sfsuphysics Supporting Member

    Viet, you absolutely can use DI without the RO part, however if your your DI resin will get used up on the order of 20 times faster without an RO membrane. Now if you have really clear water to start with this probably won't be much of an impact, however if you have a more "normal" level of TDS in your water supply you'll go through resin faster than you think.
  15. GreshamH

    GreshamH Guest

    what both said above but would add just DI could expose you to things like copper, lead, pesticides, etc. Check with your muni and see what your source is like. I'd also test your house output using one of the many water labs (not cheap, but neither are our tanks)
  16. screebo

    screebo Supporting Member

    My tap water is 30 ppm of disolved solids. My RO water is 10. Interesting enough, I do have a portable "car wash" style resin system and lots of extra resin. Would it be worth it to plumb it up under the sink? If so, I'm guessing I'd place it ahead of the RO system.

    Bigger question: How much difference, if any, will bringing my TDS down below 10. What I mean is that if I get 95% of the results from 10 ppm water as I would from 2 ppm water then I wouldn't think it makes sense to chase it down.
  17. sfsuphysics

    sfsuphysics Supporting Member

    Hmm, I'm guessing your TDS meter is out of whack (often an issue for the very low readings) or your membrane is out of whack, because going from 30 to 10 is only a 66% rejection. IMO those portable DI resins probably wouldn't be worth the trouble, the Mr. Clean version? :D

    If you haven't had any sort of algae issues or what not, i wouldn't even bother chasing it as low as you can to be honest.

    .... now the real question is why the hell are those TDS meters always set to use those damn watch batteries that cost a fricking fortune!
  18. screebo

    screebo Supporting Member

    Great point, Mike. I'm gonna test some distilled water and see what it shows! I'm with you about plumbing up any additional gear at this point. I'm gonna hold off for now. Algae? Sure, I've gone in and out of algae issues. Right now I'm still going through the new tank algae cycles. All in all, things look very clean and livestock is thriving. I recently plumbed up a Two Little fishes Phosban reactor and it's chuggin' away in the sump. I think I'm good to go with wading through some continued algae/diatom blooms until it REALLY is done with cycling. It will help that I'm done adding the heavy load livestock for the time being............:cool:

    Side Note: speaking of measuring instruments, I'm waiting for the replacement probe for my Pinpoint II calcium monitor. The first probe would not allow the unit to calibrate properly. Anyone else using this instrument? Last evening, I found that with my tryed and try chemical test method, I was running low on CA so I adjusted to bring it up to 440. Gotta be a friggin' scientist, in my case a bit of a mad scientist.

    There is good news: With input from more stable types, I've gone from making WAG's to SWAG's
    (Wild-Ass Guess vs. Scientific Wild-Ass Guesses)
  19. GreshamH

    GreshamH Guest

    Unfortunately PinPoints are not known for being 1. accurate 2. built well. We use them as nearly disposable units where I work and only to get a rough estimate.
  20. Gomer

    Gomer Honorary Member

    but if you get 10 of them, you can use the average!


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