? Relationship Between TDS and Hardness.

Discussion in 'Water Softener Forum, Questions and Answers' started by sidmoore, Aug 11, 2013.

  1. sidmoore

    sidmoore New Member

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    Aug 10, 2013
    Location:
    Comanche, Texas
    Well, I understand that a TDS reading lumps all dissolved solids together and that these, mainly, consist of calcium and magnesium. It is also my understanding that "hardness" is a measure of the amount of calcium (mainly) in the water. What I don't understand is: How can one possibly derive a reasonably close hardness estimate from a TDS reading? Witness my latest conundrum.

    I came to realize that our water softener was no longer softening and decided that I had been pushing its capacity by running scheduled 1100 gallon cycles (this is a Culligan Twin 9100 with a Fleck controller), so, I figured a good first step was to do a few "on-demand" regens and did two for each tank. The practical result so far is the fact that the water now has that "slippery" feeling of softened water when showering. However, my pocket HM Digital TDS meter now reads about a hundred points higher (before: 640).

    So, my main question is: How useful is a TDS meter for measuring water softener performance?'

    Second, if not a TDS meter, what can I, as a homeowner, use to measure hardness?

    Thanx for listening!

    Sid
     
  2. Tom Sawyer

    Tom Sawyer In the Trades

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    A TDS meter is pretty much usless for calculating hardness. You need a Hatch 5B kit, about 30 bucks on amazon.
     
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  4. mialynette2003

    mialynette2003 In the Trades

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    TDS will in fact be higher on soft water than on hard. As Tom said, a Hach 5B is a very good kit for testing hardness.
     
  5. sidmoore

    sidmoore New Member

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    Thanx for the tip, Tom. I had searched Hach for hardness kits and, for whatever reason, came up only with expensive, or, one shot kits. Much appreciated.

    Sid
     
  6. sidmoore

    sidmoore New Member

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    Mialynette, I had figured that might be true, but, had no way to really know, until you just verified it for me. Thanx!

    Sid
     
  7. ditttohead

    ditttohead Water systems designer, R&D

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    Water systems designer, R&D, Technical Director
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    Ontario California
  8. sidmoore

    sidmoore New Member

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    Aug 10, 2013
    Location:
    Comanche, Texas
  9. David A.

    David A. New Member

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    TDS meters read electrical conductivity (EC), which is related to charged particles in the water (ions). TDS stands for total dissolved solids, but that's not completely accurate, since non-charged particles don't increase the conductivity of water (such as oxygen, nitrogen, and any nonpolar molecules that don't dissociate in a polar solvent).

    There is a relationship between hardness and TDS (1 grain = 17.1 PPM), so the harder the water, the higher the TDS reading. But since the TDS meter can't distinguish between calcium and sodium, it's not a direct correlation, so you can't say 34 PPM = 2 grains of hardness because some of that will be calcium but some of it will be sodium, potassium, etc. And since 2 sodium ions replace each calcium ion, your TDS will increase after softening.
     
  10. Bannerman

    Bannerman Active Member

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    Not sure why an almost 4 year old thread is now being replied to. Sidmoore has not visited this site since March 2015.
     
  11. ditttohead

    ditttohead Water systems designer, R&D

    Joined:
    Jan 9, 2012
    Occupation:
    Water systems designer, R&D, Technical Director
    Location:
    Ontario California
    Very odd. Oh well, I will add another thought. In general, TDS is not an accurate measurement as it is more accurately just an algorithmic estimate. conductivity and resistivity are actual measurements. TDS is estimated from these actual numbers but since TDS is more easily understood it has become the standard.
     
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