TDS reading through RO unit

Discussion in 'Water Parameters and Additives' started by deadmeat2016, 5 Mar 2013.

  1. deadmeat2016

    deadmeat2016 Wouter

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    What is the average level of dissolved solids in water from an RO unit? our tapwater is around 85ppm, the RO unit consists of 4 stages, 5micron sediment filter, granular activated carbon, carbon block and then the RO membrane. The reading im getting from the RO is around 25ppm.

    Is this normal? or is it still too high? I just changed the filters today.

    Got the meter today and also a bit of DI resin in a chamber to add it to the RO unit.

    The RO unit has a 10l holding tank, should i connect the DI after or before the holding tank or after it(so it runs through the resin before it comes out the tap)?
     
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  3. Trasique

    Trasique tahir

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    the DI resin could be to blame
    how old is it, and was it moist when u replaced it. @The Waterboy - Marco is the expert
     
    Last edited by a moderator: 26 Nov 2015
  4. deadmeat2016

    deadmeat2016 Thread Starter Wouter

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    Havnt added the resin yet
     
  5. Nemos Janitor

    Nemos Janitor

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    Did you rinse/flush the sediment and carbon block before you replaced the RO membrane? What membrane did you use? 50, 75, 150 gpd? Was it the same as the gpd membrane as before? What flow restricter do you have?

    Sorry for all the Q's but there could be a number of causes.

    DI resin straight after the RO membrane.
     
  6. Nemos Janitor

    Nemos Janitor

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    Are you measuring the TDS straight from the RO membrane?
     
  7. deadmeat2016

    deadmeat2016 Thread Starter Wouter

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    no worries, I didnt check the membrane.....feel a bit stupid now but i think it might have been a 150gpd

    And was busy flushing them and reading has dropped to 20ppm, should i really have the DI resin before the storage tank? the dude i got it from is a specialist and says have it after because DI water doesn't store very well. I am still new to the resin and will have to top it up at some point or perhaps get a bigger canister for it but i just hooked it up after the storage tank.

    Where is Marco when u need him lol
     
  8. Visser

    Visser MASA Contributor

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    The "specialist" is talking BS!
    If you put the resin after the canister, it will force the water through the resin quicker than it can absorb the solids, leaving you with a high output tds reading...
    Oh, & 0 tds ro water stores just fine! In fact, it stores much better than any other water as there is absolutely nothing in the water that can "poison" the water...
    The only thing that might contaminate ro water could be if the canister is rusted or contains sometimg in the internal coating of the container that gets dissolved through diffusion... There is also no organics in 0 tds water that can contaminate/leach ammonia & nitrites into the watet...
     
    Last edited: 5 Mar 2013
  9. RiaanP

    RiaanP Moderator

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    RO units for humans have those holding tanks with internal bladder. You sure yours is not a incorrect?
     
  10. Nemos Janitor

    Nemos Janitor

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    Bud the flushing of the pre filters prevents contaminating and blocking the RO membrane. Always flush the prefilters for at least 10 minutes before connecting to the RO membrane.

    The RO membrane also needs to be flushed. The first 200L of water should be discarded.

    The flow/flush restrict or is pared with the membrane. So you need a 300 flow valve for a 50 gpd membrane and a 800 for a 150 gpd membrane.

    RO water does attract solids from the atmosphere however the reason is probably due to the container containing dissolved irons.

    I would also not recommend using a 10l holding tank on a 150 gpd unit. The membrane will block very quickly and you will use a tremendous amount of water on flushing. It is always best to make a batch of at least 100L at a time. You will preserve your membrane and save water.
     
    Last edited: 5 Mar 2013
  11. RiaanP

    RiaanP Moderator

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    Not really. Because there is nothing else in the water, a open RO container can easily absorb chemicals, flavours and aromas from the surrounding environment. Can test it in your fridge. The water will taste after a day or two like whatever have the strongest flavour in your tank.
     
  12. Visser

    Visser MASA Contributor

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    True, but 0 tds water will absorb almost as much as 20 tds water... Only when you start getting to levels where that water contains more chemicals than that absorbed into the container will it stop leaching chemicals into the water though diffusion. In my opinion, its an ignorable factor.
    For example: my ro tds reading going into my 500l container is a dead solid 0 & my outlet water after standing in the container for more than a month is 1-2.
     
    Last edited: 5 Mar 2013
  13. deadmeat2016

    deadmeat2016 Thread Starter Wouter

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    rahhh, what i did was flush the all the filters for about 45 mins, added the resin after the storage tank. Will update on how this goes, but either way i should expect the first 100L or so to be a bit higher than usual in TDS then? Will flush it a couple of times, the waste from the RO membrane is controlled electronically, will post pics tomoro. Gonna flush a couple of times and then take a reading, remember that i got the DI resin and canister as a sample, can always position change later. I will go back to the place i got the membrane from and have a look at the gpd rate. Still want Marco's 2 cents......

    Oh and incase the membrane is contaminated, i will change it when i change the sediment filter, which is every couple of weeks because our water here in gbay has alot of sediments.
     
    Last edited: 5 Mar 2013
  14. Visser

    Visser MASA Contributor

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    Please do. Will be interesting to see your results.
    Can you please try one thing for me... After your setup has completed its 200l startup...
    Please take a tds reading with the water running at a drip rate (after 2 min dripping) & then again after you opened the tap 100% to see if the resin after the container will have detectable tds..
    Thanks
     
  15. Nemos Janitor

    Nemos Janitor

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    Bud we may be misunderstanding each other. The pre filters release fines that block the RO membrane. Mostly the GAC dust from the carbon block. A membrane can block in a few days if the carbon block is a dusty one.

    If you have a lot of sediment in your source water, then per filter with a few sediment blocks before you feed the RO unit. This saves the RO membrane which is the expensive part. This is also recommended or bore hole water.
     
    Last edited: 5 Mar 2013
  16. deadmeat2016

    deadmeat2016 Thread Starter Wouter

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    Hey guys,
    Thank you so much for all the help, I think i now know a bit more of what i am doing, gonna replace the RO membrane again in 3 weeks, but for now......TDS reading is 1, the DI resin works!
    gonna update on the progress if anything changes
    Thanks again
     
  17. Visser

    Visser MASA Contributor

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    Please please dont replace the RO membrane... Those membranes can last up to a year. (sometimes more depending on usage)
    Keep it until your tds reading directly out of the membrane climbs higher than +-40-50 ...
     
  18. deadmeat2016

    deadmeat2016 Thread Starter Wouter

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    Thanks dude, that sounds more economical. Just a bit afraid of wht janitor said and the RO membrane becoming clogged, RO is such a mission lol :) Will take a reading in a week or so

    O and my system is a 1000L so uses like 2-4 liters per day
     
  19. Nemos Janitor

    Nemos Janitor

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    The TDS will not drop but the flow will decrease. You will end up making very little RO and a huge amount of waist water. If you are happy with the volume of water the membrane is making then leave it until either the volume becomes unacceptable or your TDS is high.
     
  20. deadmeat2016

    deadmeat2016 Thread Starter Wouter

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    ok! thanks guys
     
  21. Suhayl

    Suhayl

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    Your tap water good and you should get 0 tds out of your ro unit without the di resin, something wrong there. My tap water tds 360 and I get 0 tds readings without di resin. I use cheap brand filters and they seem to work for me. To get longer life out of the membrane I change sediment and carbon filters every 6 months. Do away with those storage tanks that come with the household ro units as they make your tds readings go up again.
     
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