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  1. #1
    Senior Member
    Join Date
    Jan 2004

    Membrane and TDS?

    What is acceptable TDS? I know 0-0001 is prime but what is the reading that tells you it's time to change your membrane?

  2. #2
    Senior Member reefmutt's Avatar
    Join Date
    Oct 2003
    That's an excellant question and I don't really know the answer in terms of a number. All I can say is that if you have a tds meter and you've been getting the same reading for a long time from your r.o. unit and sudenly the readings start to climb, it means that your membrane is failing- this would be the time to change it, I think.

    Old system torn down to make a playroom.. planning a 62x42x28 high

  3. #3
    Senior Member Aqua's Avatar
    Join Date
    Jan 2004
    Efficiency of RO membrane is ~90% best case ~95% so if you measure TDS of water going in and out of your RO unit without any filter or DI it will tell you if it is time to change it.
    Input 100 ppm, output 5-10ppm your membrane is good.
    Input 100 ppm, output >20ppm your membrane is at the end of life so it is time to change.
    Also donít forget to flush membrane regularly otherwise efficiency will go down and you may get high reading from perfectly good membrane.
    For water that is 0 or near 0 TDS you must have DI cartridge after your RO membrane and that has to be changed on regular basis depending on capacity of cartridge. Using TDS meter you can tell if it is time to change your DI cartridge.

    Anyway properly maintained (flushed regularly) and regular change of pre-filters expect ~5years from RO membrane.
    Man that goes to bed with itchy butt, wakes up with stinky finger!

  4. #4
    ijo is offline
    Join Date
    May 2011
    In addition to the above.. if you have one of those dual inline TDS meters... its a good idea to connect the input line right after the RO... and the other after the DI... this way you can tell when its time to change your RO membrane and when your DI needs a change. I found the input line conected to the house water was wasted as it rarely ever changes. HTH


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