KH <= GH

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

  1. Oldguy

    Oldguy Member

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    Most plant enthusiasts want 'free CO2' in their tanks so that non obligate aquatic plants can grow well under water. We blow CO2 into the water to feed the plants and try not to gas the fish. High buffering at pH 8 ish makes this difficult to achieve. Lower buffering at pH 8 or lower enables more CO2 to be 'free' especially at pH 6.8 and lower and lower buffering enables this to be achieved. This buffering is typically expressed as bicarbonate buffering but in practice is the sum of a thousand and one different ions. Eg the aqueous sulphate ion has a pH of about 7.4. The planty folk also pour dihydrgen phoshates into their tanks which will dissociate into both mono and di salts and form a strong pH buffer. Rain water and purer has little buffering capacity but the water in our little glass boxes has.
     
  2. Edvet

    Edvet Global Moderator Staff Member

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    pH swings due to CO2 is a weak acid reaction, these are virtually harmless to our animals. Wanting to keep pH constant can lead to dangerous measures.
     
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  3. sciencefiction

    sciencefiction Member

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    Not a chemist but from my own research on the same:

    Total Alkalinity = [HCO3-] + [OH-] - [H+]

    Total alkalinity(buffering capacity), is not directly related to dGH.

    On another hand pH is expressed via the formula [H+] = 1x10^-pH which means the more [H+] in the water, the lower the pH, the lower the alkalinity. The higher the [HCO3-] + [OH-] , the higher the alkalinity, the higher the [OH-], the higher the pH.

    German Carbonate Hardness or dKH = [HCO3-] +[CO3^2-]

    or it is expressed in ppm of CaCO3 and is directly related to dGH in the meaning that dKH cannot be higher than dGH because dKh is part of the measurement of dGh
     
    Last edited: 1 Dec 2018
  4. sciencefiction

    sciencefiction Member

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    Following my above post, adding CO2 to water generates

    1) CO2 + H2O <=> H2CO3
    2) H2CO3 <=>[ H+] + [HCO3- ]

    It does decrease pH due to the addition of [H+], however, it does not alter total alkalinity because it results in equal [H+] and [HCO3-] cancelling each other. It is the reason why fish are not bothered by swings of pH due to addition of CO2. However, fish would be affected by a massive drop of total alkalinity or when you have high [ H+] concentrations and low or non-measurable [HCO3-] + [OH-] (for example adding strong acids) , meaning your water is non-balanced and totally out of whack....So in essence, you do want a measurable total alkalinity or what we've become to know as KH, which naming isn't technically correct. as explained in my previous post, but regardless of its name, one should aim at some measurable level in the tank....
     
  5. zozo

    zozo Member

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    What draws me off in this view is my water company report.. :)
    They measure HCO3 in mg/l, Total hardness in m/mol, not in the report but via an other route on the website i can lookup the dGh
    and they give a dGh 6 on my adress.

    If i look up how many mg/l = 1 dKh is correponds with the report
    Same as how many m/mol is 1 dGh corresponds with the report.
    In this sum the result is a Higher Kh than Gh.

    If the statement if dKh is higher than dKh = dGh than my water company is taking me for a ride and i do not have soft water. Than their website should simply say i have 10dGh but they don't...

    I'm not confident enough in the matter to give the water company a call to dispute their report.. But i know a Chemsitry teacher... And i saw and asked him yesterday what he tought about the statement.. He looked at me with googly eyes and couldn't answer it straight away.. He said something like it's the way you look at it but it still are different things.. So there probably is no straight answer.. Or it is to difficult and boring to explain while playing a game of cards. :)
     
  6. sciencefiction

    sciencefiction Member

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    Where do you get dGH6 from?

    From what I checked mmol/l is converted to mg/l by multiplying the mmol/l value by the molecular weight of the component in grams so 1.09 mmol/l could be hundreds of mg/l.
    From the way your report is presented, carbonate hardness is part of the that same total hardness of 1.09 mmol/l, which is the point in this thread.
    So your water may not be that soft at all looking at that report...
     
  7. zozo

    zozo Member

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    From my water companies website.. :)
    And a drop tester gives fairly the same result.

    If i send my water company an e-mail they send me the latest lab report. In this report no gH is mentioned, they state total hardness in mmol/l

    https://en.wikipedia.org/wiki/DGH
    My WC Report - Total hardness = 1.09 mmol/l / 0.17832 = 6.1 dGh.. :)

    all this with 190mg/l HCO3 which equals 10 dKh.. Kh drop tester gives me the same result..

    Than if the statement is true Kh = Gh than my water company is juggling and hussling with numbers to present their water softer than it realy is..
     
    Last edited: 1 Dec 2018
  8. sparkyweasel

    sparkyweasel Member

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    I think water companies only consider calcium and magnesium as hardness. And carbonate as alkalinity if they bother about it at all.
     
  9. jcspotless

    jcspotless Newly Registered

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    I suspect the water company reports reflect the test methods in place. I have not worked for water company but have conducted analysis for bicarbonate (HCO3). I don't know what current methodology is but a quick google seems to imply they still use the traditional titration method for alkalinity for KH whereby a strong acid (HCL) is titrated to a fixed pH inflection point pH 4.5 to represent amount present is this then converted to units equivalent to millimolar of a given ion (HCO3). There are method to measure anions in solution directly (such as ion chromatography) but these have the disadvantage of being specific for target ions whereas the more traditional methods do not differentiate between the various anions which might be present. As sparkyweasel says total hardness may just be a measure of Cations (Mg and Ca) but expressed in units of mole equivalents of CaCO3 (mole weight 100.09)
     
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  10. jcspotless

    jcspotless Newly Registered

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    Attached is water report from Affinity Water. It shows a hardness value of 330 (units mg CaCO3)/L) and Calcium value 132 (mgCa/L) . These two values may derived have same route value since difference between 330 and 132 is same as difference in formula weight (100.09 CaCO3 vs 40.078 Ca). In fact report says a single sample collected for each. I guess my point here is these values shouldn't be taken too literally as I suspect they are derived values based on requirement of analytical methods in place. Interesting I could not find published methods, it looks like to me. Its the ISO standards which (or their local equivalents, e.g BS std in UK) which are followed. I did find an old Swedish ISO standard which does provide some detail on how alkalinity method works. Attached for those interested. Current ISO std is version 2 not 1 but hopefully basics are still the same.
     

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  11. jcspotless

    jcspotless Newly Registered

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    I can see how people may attempt to modify pH which they believe is effecting fish or plants. Surely a buffered system (with high ionic strength) will return to the pH pretty quickly to a pre-determined set point. Phosphate buffers at around pH 7. Bicarbonate higher. Injections of CO2 might change the equilibrium but if the ionic strength is high enough these anions will return the pH to a set point which is determined by the pKa of the substances in solution. Absence of the buffers (phosphate, carbonate etc) i.e a lower KH will lead to CO2 rapidly changing the pH. Hence my statement why does anyone want low KH. The concentration of CO2 and its ionic equivalent in solution can still be high (and presumably feed the plants). Given the very low concentrations of other elements Fe etc again I struggle to see a downside. Fish I assume do not like change in water conditions but how affected are they by hardness, I am skeptical. Maybe the ratio of Calcium and Magnesium is significant? Since calcium and magnesium might be biological involved in same processes I can understand how this may affect living systems. In low calcium and magnesium systems how to fish maintain a healthy blood chemistry (another argument for high KH :)?)

    Interested to hear opinion or better still facts.
     
  12. Edvet

    Edvet Global Moderator Staff Member

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    Reproducing the natural environment of many tropical fishes, though not always neccesary, can be better to induce breeding and /or replicate their natural behaviour. For instance blackwater habitats have low natural pH and very low conductivity. (ph range 4-5, <20 microsiemens).
     
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  13. Edvet

    Edvet Global Moderator Staff Member

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    In Ukaps terms i believe having a pH controler influencing the CO2 delivery ( stryving for a constant pH) will lead to unstable CO2 levels, which will lead to algae. Having a pH drop from 1 point, which we generally advise in high light situations, is harmless for fish.
    There is discussion wether the 1 point drop will be correlated to the same CO2 level in harder and softer water. I believe softer water will need higher drops, but others believe it doesn''t matter within the most used waterparameters.
     
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  14. dw1305

    dw1305 Expert

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    Hi all,
    It is the ionic strength that is the interesting bit, soft water has very few ions of any description, and any addition of weak acids (from dissolved CO2, humic compounds etc.) will reduce pH. If this water is vegetated then we have will have large diurnal variations in pH, because of the lack of carbonate buffering. There are values (and a scientific reference) in this thread <"TDS and remineralising.....">.

    You can start with low conductivity water and then replicate these conditions by adding humic substances. A good review article of this is <"All the leaves are brown">, this references Dr <"Christian Steinberg"> who is a leading researcher on the ecological role humic substances in fresh and marine water.

    If you start with hard water (high ionic strength) you can reduce the pH with an addition of acids, or you can buffer the pH to known value with phosphate (or citric acid/citrate) buffers, but you still end up with water with a high ionic strength (in fact you've added even more ions), but lower, or stable, pH. Long term experience of fish keeping has shown that this type of water is still unsuitable for the long term keeping and particularly breeding soft water fish.

    As you approach pure H2O (rather than the weak salt solution, with H2O as a solvent, which we usually call water), pH becomes less and less meaningful as measurement, and because of this I'm more interested in conductivity, partially because it is linear scale from DI water to full strength sea water, and partially because a relatively cheap conductivity meter will give you an accurate reading without requiring calibration before every use etc.

    If you want harder water things are a lot more straight forward, you just have to add calcium carbonate to raise the pH to a relatively stable pH8.

    cheers Darrel
     
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  15. zozo

    zozo Member

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    Not completely according how the Germans explain their view of Water hardness and how to interpret the term.

    https://de.wikipedia.org/wiki/Wasserhärte

    Gesamthärte - GH- Total hardness = The concentration of cationes of <alkaline earth metals> in the water. Generaly Ca and Mg

    Carbonat-Härte = KH = concentrations of Hydrogen Carbonates anions, the equivalent part of cationes of alkaline earth metals is the Temporate Carbonate Hardness. That's the Calcium carbonate - carbonic acid - carbon dioxide equilibrium. And if you heat it, CO² escapes and Calcium deposites.

    They have a 3th one that is not commenly used so it doesn't realy come with an abriviation.(nKH?)

    Nichtcarbonat-Härte - Non Permanent Carbonate Hardness or Lasting Hardness = The Total Hardness from anions that are not bound to Hydrogen Carbonates and can not be removed.

    Somewhere in 2007 they realised the confusement it actualy gives and introduced new regulations of the hardness ranges.
    in mmol/l

    Am i correct to assume that only if KH is made up from equivalent cations T-KH than it is also GH?
    But if i take for example Demineralized water (0 in any hardness) and only add Bicarbonates i add KH but no GH since i don't add any alkaline earth metals?

    And that the confusement indeed is a mistranslation or more to say a misinterpretation of termology? (Gesamthärte = Total Hardness)
     
    Last edited: 3 Dec 2018
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  16. zozo

    zozo Member

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    Sorry that should be "Non Carbonate Permanent Hardness".. :)
     
  17. zozo

    zozo Member

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    Another one.. :)

    Knipsel.JPG
    Obviously as a play of words maybe... :rolleyes: Even if certain elements physicaly are not present, than there still is a total hardness.. Thus if there is nothing to determine GH and KH is measured than KH is considered GH.

    Found the red hering.. :lol:
     

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  18. dw1305

    dw1305 Expert

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    Hi all,
    Depends on the fish, a lot of "soft water" fish can be maintained in hard water, but they often can't breed successfully.

    Some "black-water" fish can only be maintained in soft acid water. This may relate to their inability to survive in environments with a high bacterial load, because the acidic, oligotrophic habitats have a very limited, and specialised, microbiota. That is one reason why you get the build up of dead leaves and woody material in black-water conditions, rates of decay are very slow.

    In some cases the addition of humic compounds, particularly ones with ion-exchange capacity, can lead to successful egg hatching, although the exact mechanism isn't known. This technique is commonly used with cave nesting fish (like Apistogramma megaptera and Poecilocharax weitzmani), where <"long strand sphagnum peat"> is inserted in the spawning cave, pre-spawning. With catfish like Corydoras spp. and the more demanding L numbers, then <"Alder (Alnus gutinosa) "cones"> are often added to the spawning tank.

    It is thought that the high levels of dGH cause a toughening of the egg coat and this stops successful egg development.There may also be issues with "nephrocalcinosis", in fish although this can also be associated with elevated CO2 levels.
    It is just because they evolved in situations with very low levels of alkaline, and alkaline earth, metal cations. Since the widespread use of RO units fish like Discus have been much easier to maintain.

    As a general rule you can't maintain hard water fish in soft water, but it is usually less of an issue, because it is much easier to add substances to water, rather than take them away.

    cheers Darrel
     
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  19. dw1305

    dw1305 Expert

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    Hi all,
    I think they do.
    They are.

    The calcium value will sometimes differ, because it has been measured via ICP, but usually they are all derived units.

    There isn't much magnesium in most British tap water, <"for geological reasons">. In the UK you can assume that alkalinity, dGH and dKH all relate directly to dissolved CaCO3. Conductivity is also mainly a reflection of geology, although if you

    This isn't true for New Zealand, <"or Lake Tanganyika">, where volcanic activity has led to very different water composition.

    cheers Darrel
     
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  20. sciencefiction

    sciencefiction Member

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    Yes, because when you add soda bicarbonate, you only add [HCO3-] and [OH-], but not Ca2+ or Mg2+ , so dGH remains unchanged. But even when adding soda bicarbonate, you'll have a really hard time moving the KH up more than 4 dKH or so...It would take lots of soda bicarbonate :lol: The pH will go up due to the addition of [OH-],, but then again....because GH is not changed, fish could not care one bit about the upward pH swing for that same reason,,, Hence pH is an irrelevant measure and it only matters as a guidance, to give a general idea of how hard one's water is...but on its own, without knowing the rest, it means nothing....In certain scenarios one can have high pH and soft water and low pH and hard water, although the opposite is true as well in majority of cases.

    If you add soda bicarbonate to soft water, it will not make ones water any harder because there's no Ca2+ or Mg2+ involved. However, adding soda bicarbonate means an addition of [OH-],which will level out the [H+] and bring the pH back up, thus balancing the water. It doesn't need to be balanced back to a neutral pH, it just means that there's enough [OH-] for the tank to function correctly. Old tanks tend to become acidic,....so addition of bases is essential, normally via water changes and not soda bicarbonate :)

    I have had a scenario when my pH plummeted down, KH zero-ed out, the GH remained unchanged, TDS was through the roof, fish were gasping...So I don't measure GH ever anymore. I reckon TDS and KH are the only measures worth monitoring in a tank...Any movement up and down, there's an issue in the tank that will show up as weak fish/fish diseases.......
     
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