High TDS reading

Discussion in 'General Discussions and Advice' started by JD167, 17 Aug 2010.

  1. JD167

    JD167

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    Hey guys, hope you can shed some light on this problem i'm having.

    Lately I'm having some GHA growing on the sides and back of my DT. Not a lot but enough to make me worry. I have a new RO unit and testing the water with a TDS meter shows a reading of between 1 and 3. I made up a 100L drum of RO and tested the RO as it's flowing into the drum. It stays at 2.

    So after it filled up I leave the drum for about 8 hours and last night I test it again. TDS of 3. So I dump the 12000L/h pump in the drum and off it goes. 5mins later I test again and it's sitting at 70!!! It's plain RO with no salt added yet.

    I just don't get it. Could it be the pump? The RO drum was empty when I started filling it. If the drum was dirty, surely it would have shown in the reading before switching on the pump?

    Any ideas?
     
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  3. Drk

    Drk

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    Did you rinse the drum out with RO water before filling it up?

    Did you run the RO unit for ten min discart that water and then fill up the drum?

    When did you last replace the RO unit filters?
     
  4. Manic

    Manic Moderator

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    Do you use the same pump to mix the salt. Reason for asking is that the pump may of had some salt still in it and that dissolved in the water.
     
  5. TheWaterboy

    TheWaterboy Sponsor

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    very odd
     
  6. mariusmeyer

    mariusmeyer

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    I'm thinking salt on the pump.
     
  7. TheWaterboy

    TheWaterboy Sponsor

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    or faulty t.d.s meter......
    but salt in the pump sounds more likely.....

    what unit is it and what t.d.s meter is it???
     
  8. Manic

    Manic Moderator

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    Just a warning that TDS meters are sensitive to magnetic interference. Maybe turn the pump off and try again with the pump out the water. I tried testing my TDS once and it was around 300 just because I was checking it close to my MH ballast.
     
  9. TheWaterboy

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    very true
     
  10. JD167

    JD167 Thread Starter

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    The name of the pump escapes me, but I think you are right. I tested the TDS this morning again and it was around 61, down from 70. The pump was still in the water. I'll check it again this evening. I'm going to Frans later so I'll take a sample with and test it with his meter.
     
  11. FransSny

    FransSny

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    JD as we discussed , the salt precipitation in the cannister & maybe on the pump is causing the error on your TDS, meausred 0,66 by me with error warning on my TDS.

    I am also not sure why this is of concern as your "make up water" is good
     
  12. JD167

    JD167 Thread Starter

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    That's what is so strange to me. One minute it's reading 2 the next 70. If the theory of salt precipitation is correct it would explain why the TDS reading is out. I'd hate to throw away 130L of RO for nothing.

    I think I'm going to try one more test by putting 20L of RO in a bucket and then placing the pump inside and measure the TDS.

    Thanks for testing Frans.
     
    Last edited: 18 Aug 2010
  13. lIghty

    lIghty

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    I would also say salts on the pump.
     
  14. Ash

    Ash Coral biologist

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    this may be a stupid question but I've never used TDS meters before. What are u testing for? conductivity? IE the amount of dissolved organics as ions in the water.
     
  15. FransSny

    FransSny

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    not a stupid question ash , yes basically TDS meters are conductivity meters. TDS refers to the total amount of dissolved solids in the water, (unless you can evaporate & wheigh what is left to measure) a tds pen is used to measure conductivity and thus estimate dissolved solids
     
  16. Ash

    Ash Coral biologist

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    But what benefit would that reading be? Is it a short cut rather than doing all the usual WQ tests?
     
  17. FransSny

    FransSny

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    No it is different to "normal routine water tests", there is a website dedicated to tds meters , what they do etc (sorry cant recall the name) Higher TDS readings (than accepted range) indicates a higer amount of mobile charged ions (salts, minerals etc)

    These could lead to issues such as PO4 spikes etc wich we would pick up with test kits

    Hope this makes sense
     
  18. Manic

    Manic Moderator

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    The TDS meter is used only to test your RO water and nothing else.
     
  19. Ash

    Ash Coral biologist

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    It does. Ye, using it on salt water wouldn't give you any useful info I'd imagine. It would simply be overshadowed by the conductivity of the salt.
     
  20. lIghty

    lIghty

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    Yip, like Manics said, it only used to test the RO water for topping up evaporation on a closed system, to ensure it is free of desolved solids like PO4.
     
  21. Ash

    Ash Coral biologist

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    cool. all cleared up. Thanks
     
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