Sand's affect on ph?

Discussion in 'Water Chemistry' started by Grant, Sep 28, 2009.

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  1. Dingo

    Dingo Giant Squid

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    I have class until 1... Once I get home I will pull out some old equations I derived for buffering compacity and pH from a few years ago. In the mean time it won't hurt to try lunas suggestion.

    If that doesn't work I will post the equations and how to use them so we can use them in the future.
     
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  3. Grant

    Grant Feather Duster

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    Great.

    Since I'm off work today and tomorrow, I have some time to work on my tank :) So I think I'm gonna start the process of replacing my cc with sand. Even if this doesn't solve the ph mystery, I've kinda wanted to do this anyway. And from what I've read so far, it sounds like a good move for other reasons too. And it will at least take out one questionable variable in the ph mystery. I'll get an airstone pumping asap too. Wish me luck.
     
  4. lunatik_69

    lunatik_69 Giant Squid

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    Before buying anything, ask your LFS if they can test your water for O2 levels. If not, Salifert sells a O2 test kit.



    Luna
     
  5. lunatik_69

    lunatik_69 Giant Squid

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    Here it is, it costs around $20.00
    [​IMG]
     
  6. Grant

    Grant Feather Duster

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    O2 test results: 5 mg/l

    according to the test kit (Tetra, all my lfs had), this is in the acceptable range for my given temp and sg. On the lower side of range, but within the acceptable range.
     
  7. Dingo

    Dingo Giant Squid

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    well i got distracted on campus and got home a little later than planned... neways, im working on this now so hopefully i can turn up an answer!!!
     
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  9. Dingo

    Dingo Giant Squid

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    does your alkalinity test give a value for dKh or does it give you concentration CO3?
    and what is the exact value you are getting?
     
  10. johnmaloney

    johnmaloney 3reef Sponsor

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    does it really break down at a normal ph? I though that was for only low ph, (reactor style) environments. (I am back at a page 1 still). :)
     
  11. Daniel072

    Daniel072 Giant Squid

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    John, from everything i have read and experienced, it does NOT break down at normal ph. If the ph in your DT gets low enough to break down aragonite, you have other issues on your hands.
     
  12. Dingo

    Dingo Giant Squid

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    Success lol (i hope)

    So we have
    pH = -log(Ka) - log([HA]/[A-])
    we have the log of ka which is pKh minus the log of the acid concentration over the conjugate acid concentration.

    after some substitutions for final buffering compositions, in the equation above you will come to this... lowest possible pH is 6.4, highest possible pH is 12.8
    now for the molecular weights of the molecules of interest. HCO3 is 61 and CO2 is 44 (used in conversion to german degrees: dKh)

    substituting in and rearranging a little you get CO2 = 12.8 * dKh * 10^(6.4-pH)

    usefully arranged for our application as:
    pH = 6.4 + log[(12.8 * dKh)/CO2]

    CO2 is the concentration of CO2 in water... since we dont have a test, we can plug and play.
    Currently, at pH 7.7 with dKh of 11, your [CO2] is 6.605. when translated to german degrees it has a value of .1501

    as luna said, increasing the [CO2] makes lower pH:
    pH = 6.4 + log [(12.8 * 11) / 10] pH = 7.51

    to get pH 8.2:
    pH = 6.4 + log [(12.8 * 11) / 2.13]
    NOTE: this is only at dkh of 11. as dkh rises, so will pH

    so in summary, you will need to reduce the concentration of CO2 (mg/L) in your tank from 6.605 down to 2.13, or raise your dKh to a higher value to buffer at the pH of 8.2.
    this probably didnt help but now you know lol

    do you use a type of algae in your sump (like cheato)? if you light it 24 hours this will constantly undergo photosynthesis and in turn pull a lot of CO2 out and also give off O2 as a bi-product.