KH <= GH

Discussion in 'Water Chemistry' started by Edward Shave, 19 Nov 2018.

  1. Edward Shave

    Edward Shave Member

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    A short time ago A thread I started in another place was closed down by a moderator because I was arguing that KH can never be greater than GH. In fact the moderator went so far as to say this was nonsense.

    Now this really threw me because I'm sure I'm right....

    Since I'm posting this in the "Water Chemistry" section I'm hoping some knowledgeable person will confirm this and thus save my sanity lol.
     
  2. ian_m

    ian_m Global Moderator Staff Member

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    Can't see any deleted/closed post by you. All posts & threads by you are still open and active (or not).o_O
     
  3. Edward Shave

    Edward Shave Member

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    Apologies, I should have been clearer... By another place I meant a different site altogether.
     
  4. Andrew Butler

    Andrew Butler Member

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  5. Nuno Gomes

    Nuno Gomes Member

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    If you are sure, why do you need someone to confirm you're right?

    And you're wrong by the way, but I do understand the mixup, the General in GH makes people think GH includes KH.....
     
  6. Edward Shave

    Edward Shave Member

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    Many people including the author of this article make no distinction between KH and Alkalinity..! They are not the same. Alkalinity can indeed be greater than GH but KH cannot since GH=KH+NKH.
     
  7. Edward Shave

    Edward Shave Member

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    GH is Total Hardness. Total hardness = Carbonate hardness (KH) + non Carbonate hardness.
     
  8. Nuno Gomes

    Nuno Gomes Member

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    It's General Hardness, not Total Hardness.
     
  9. Edward Shave

    Edward Shave Member

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    Should more accurately be called “Total Hardness” as it was mistranslated from the German “Gesamthärte“. The term “Total” makes more sense as GH is the sum of carbonate and non carbonate hardness
     
  10. Daveslaney

    Daveslaney Member

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    Sorry to say but I think you just answered your own question here.
    GH= KH PLUS NON CARBONATE HARDNESS. So there for the KH can never be greater than the GH.
    But according to the link provided by Andrew GH is actually just the magnesium and calcium.
    So the KH can be higher than the GH.
     
    Last edited: 19 Nov 2018
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  11. X3NiTH

    X3NiTH Member

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    Semantics!

    Total Hardness = Permanent Hardness + Temporary Hardness

    Permanent Hardness = Chlorides + Sulfates etc.

    Temporary Hardness = Carbonates

    Total = All Ions (not just Ca and Mg)
    Permanent = Not removed by boiling
    Temporary = Removed by boiling
     
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  12. Edward Shave

    Edward Shave Member

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    The "Temporary Hardness" you refer to in your first equation is another name for Carbonate Hardness or KH. So by your definition KH must be less than Total Hardness (GH).

    Strictly speaking Total Hardness is the sum of multivalent cations so for example monovalent ions such as Na+ (sodium) are not included.
     
  13. Edward Shave

    Edward Shave Member

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    GH or total hardness is a measure of the multivalent cations present in the water. Principally Ca++ and Mg++

    KH or carbonate hardness is that portion of GH cations associated with carbonate/bicarbonate anions. Despite the name it is the multivalent cations and not the carbonate anions that contribute the hardness property.

    NKH or non carbonate hardness is the remainder of the multivalent cations not associated with carbonates.

    Thus GH=KH+NKH leading to the conclusion that KH<=GH
     
  14. Simon Hellmich

    Simon Hellmich Member

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    Is an aquarium gh test affected by carbonates?
     
  15. dw1305

    dw1305 Expert

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    Hi all,
    This is all in the the OP's (@Edward Shave), other thread, <"Boiling off KH">.
    That one. When you add a monovalent carbonate (like sodium bicarbonate (NaHCO3)) you have raised the carbonate hardness (dKH), electrical conductivity (you've added Na+ and HCO3- ions), pH and the alkalinity, but you haven't raised the dGH, because you haven't added a multivalent cation.

    The best summary of water hardness I've found are still the ones on "the Krib" <"Water Hardness"> and <"Hardness (incl. History">, mainly because they include the history and definition of the units.

    A definition of "Total Hardness" is here: <"Total Hardness">

    cheers Darrel
     
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  16. zozo

    zozo Member

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    Latest Water company report.. :)
    Knipsel.JPG

    My test kit averagely results in 11 - 12 dKh slight color switch starts at 10.

    1 dKh = 17,86mg/l HCO3 190,38/17.86 = 10,66

    This is an average report it fluctuates between 190 and 210 mg/l HCO3 (but did cut that out off the report to make the image smaller), test kit is pretty accuratly coresponding the WC report.

    My Gh test results is 6°dH, 1 mmol/l = 5,62 ºdH.. Coresponds with above 1,09 mmol/l

    1°dH = 10mg/l CaO or 10mg/l MgO
    Dunno how that corresponds with the above 32,29 mg/l Ca and 7,53 mg/l Mg i'm missing an O there and the knowledge.

    But what we can read from the test kits it seems my kH has a higher number than my gH.. :)
     
  17. Edward Shave

    Edward Shave Member

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    You are right, sodium bicarbonate will raise the value of KH but not beyond GH. What your really doing is raising the alkalinity and the two values are the same so long as KH < GH. Alkalinity on the other hand can be greater than GH.
     
  18. Edward Shave

    Edward Shave Member

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    Your test kit is measuring Alkalinity (A) not KH. A = KH so long as KH<GH. If A>GH then KH=GH.
     
  19. Edward Shave

    Edward Shave Member

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    I don't think that thread is a good example as it contains a number of inaccuracies.
     
  20. zozo

    zozo Member

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    I know that both tets are determined by adding acids and the amount of drops reflects in a pH change again in a color change. :)

    I didn't reply to discuss the issue i don't posses the knowledge i can't argue nor agree, just thought to give an example from my personal situation, that my tap water measeres kH 10 value, a higher number than the gH 6 value. Considered hard in carbonates and soft in CA and Mg.

    But obviously i'm far from understanding yuor question and point.. Sorry..
     
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