Which Kh Alkalinity titration test kit

Discussion in 'Water Chemistry' started by Zeus., 22 Oct 2016.

  1. Zeus.

    Zeus. Member

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    Hi all

    Title says it all really

    Which Kh Alkalinity titration test kit are you using or advise here in the UK

    The Red Sea KH / Alkalinity Pro Test Kit seems to be the one to go IMO

    But would value your opinon/input


    TIA

    Zeus

    Oh nearly forgot yes going for High Tech CO2 tank
     
  2. dw1305

    dw1305 Expert

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    Hi all,
    It is a case where most of the test kits will give you a reasonably accurate answer.

    This is mainly because the tests don't actually measure carbonate hardness (dKH), but <"total alkalinity">. The "proper" unit for alkalinity is "milliequivalents per litre". Total alkalinity (mg/l as CaCO3) divided by 50 = milliequivalents per litre. To get to dKH you need to multiply your alkalinity reading (in meq/litre by 2.8) = dKH (carbonate hardness).

    Because of this the kits can just use an <"acid/base titration"> with a pH colour indicator. The kit you buy has a known volume of an acid, of known strength and molarity, with a <"pH indicator"> added (usually one that goes from blue (alkaline) to yellow below pH7 etc). When you have a base (the carbonate buffered tank water) the amount of acid you have to add as a measured volume (more accurate) or drops (less accurate) will depend on the alkalinity of the water.

    Your tank water is a "weak base". If you have a weak acid (like citric acid (C6H8O7)) then you will need to add more drops (which is potentially more accurate), but you have the problem of the end point being more difficult to estimate. If you use a strong acid (this is now a "strong acid weak base" titration) then you get a clearer end point, but will add a much smaller volume of acid. I think the "Red Sea" test kit uses citric acid and, I assume, bromothymol blue as the pH indicator.

    There is a review of test kits review <"here">.
    If you haven't already it would be worth reading <"Using a drop checker">.

    cheers Darrel
     
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  3. ian_m

    ian_m Global Moderator Staff Member

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    Why do you want to know your kH?

    Plants don't care, fish don't care, most members here don't know there kH. Ok some fish spawn better in soft water.

    Most hobby kits wont give reliable repeatable results as very easily influenced by other ions/salts present in your water.

    So you get an unreliable value for kH, nice, then what are you going to do with it? Unreliably add more CO2, unreliably add more chemicals of one form or another ? Not sure having a kH value for my water would change anything I do in keeping plants and fish. However a lower kH than my liquid rock from the tap would mean less scale in my kettle.
     
  4. Zeus.

    Zeus. Member

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    Once all setup and got the experience i'm think I wont use it much. But initially I think I will. To calculate 'indirectly' the CO2 levels after all the drop checkers are slow.

    eg stet tank up, titrate get base reading, start CO2 then titrate at regular intervals. make graph check how fast CO2ppm is increasing, avoid hit and miss. find optimal CO2 levels quicker, double check with drop checker with time once tank reaches equilibrium with CO2 input. Just makes sense to me.
     
  5. ian_m

    ian_m Global Moderator Staff Member

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    Lot simpler with drop checker, mine responds within 30 minutes, not the hours people often quote. I got CO2 levels sorted by tweaking needle valve (say 1 bubble per second), at lights on drop checker blue/green, tweak a bit more seeing slight increase in bubble rate. Next day drop checker more green than blue, tweak a bit more. Next day better green tweak a bit more. Next day drop checker green/yellow, back it off. Next day green. I am using about 15gr CO2 per 8 hour period into 180litres.
     
  6. Zeus.

    Zeus. Member

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    Only just had chance to check the review you link (Sorry) - useful but a bit dated 2007, and the The Red Sea KH / AlkalinityTest Kit was reviewed, not the The Red Sea KH / Alkalinity Pro Test Kit which has a higher degree of accuracy.
    Going off The Red Sea clip on how to use the The Red Sea KH / Alkalinity Pro Test Kit was dated 2010, Red Sea data sheet for the The Red Sea KH / Alkalinity Pro Test Kit is dated 2011 but its on Version 3.

    idd, but if I am going to be using the CO2 'thruster' I have planned! might not have 30mins to wait :crazy: so having a kit would be highly advisable IMO
     
  7. dw1305

    dw1305 Expert

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    Hi all,
    I'm not a CO2 user, but if I was I would use a drop checker, purely because the 4dKH solution you use in the drop checker only has carbonate hardness, and no other source of hardness (OH- etc.).

    The only acid that enters the drop checker is the carbonic acid (H2CO3) from the dissolution of (a small proportion) of the added CO2, that diffuses across the air gap, along the CO2 concentration gradient, into the drop checker.
    It is a bit different in sea water, the water is highly carbonate buffered, and always alkaline. Because sea water is <"very highly buffered"> the pH is stable at ~pH8.2 and it is easier to separate the alkalinity due carbonates (buffering at pH8.2), from those caused by other bases (which will drive the pH higher).

    The pH8.2 is important because carbonates are insoluble in water, but soluble in weak acids (like the carbonic acid from the dissolution of CO2) and at atmospheric CO2 levels (400 ppm) water with any carbonate buffering (dKH) will have a pH of pH8.2. If you raise the level of CO2 (by adding it) the carbonate ~ CO2 equilibrium is driven towards H2CO3 and the pH falls, but this doesn't change the alkalinity.

    Additionally marine aquarists have a special problem because they have molluscs, corals and coralline algae that actively deplete the both calcium and carbonate from the water. it is slightly different for freshwater aquarists because we might have snails, but we don't have other macro-organisms that deplete hardness (although microbes will).

    cheers Darrel
     
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