Chemistry Gurus please assist...

Discussion in 'General Discussions and Advice' started by jpaige74, 22 Dec 2013.

  1. jpaige74

    jpaige74

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    At the risk of sounding like a dummy I really need some guidance in regard to Alk and pH. I really did do a lot of homework on this but I think I am still not quite grasping it. I was under the belief that Alk is a measurement of adequate bicarbonates in my system. (What my corals will use as building materials) I use a reef log program and mine has been consistently hovering at a Dkh of 10. I also believed that pH is a measurement of the soluble calcium levels in the system. My tank hovers here at 8.2.

    So here is the question. If my alkalinity is stable and indicative of calcium carbonate, and my pH is stable indicating adequate "buffers". Why is it necessary to measure the Calcium and magnesium separately? If I was lacking in either of these, would it not cause a flux in the Alk and pH as an indicator?

    My tank is currently a 55 gallon system. (recently transferred from an older 29 gallon). I have three fish. Yellowtail Damsel, clarkii, and firesfish. One large anemone, and a few small coral frags. (Hammer, leather, galaxea, and zoas) I have a deep sand bed with 4" of new sand I seeded with 4 cups of sand from the established system. I run a wet/dry canister with a protein skimmer. Aside from the pH and Alk, other test results are NH4-0, NO2-0, NO3-0. I log tests twice a week and water change 10% once a month. My display is planted with some caulerpa and 5 mangroves.

    I know to most of you this is a really silly question but Id rather sound silly and understand than take the chance of denying my livestock. I know there is a big difference between thriving and surviving.

    Thanks for your help guys and gals!
     
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  3. Visser

    Visser MASA Contributor

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  4. Visser

    Visser MASA Contributor

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    The most accurate way to describe alkalinity, is the amount of acidity required to convert carbonates, & bicarbonates to to carbonic acids...
    To make it easy... Think of it like this... The higher the alk (more carbonates & bicarbonates) the more acid you would have to add to the water to convert them to an acid... (This is how test kits measures alk... By using a type of ph test & adding acid as reactant until the liquid starts to turn acid...)

    Carbonates & bicarbs causes salwater to have a ph of 8 -8.4... Thus, as per your question... The ph isnt the buffer, but rather the alkalinity...
    If you have an alkalinity of 6dkh & higher... This will enable your ph to remain at 8+. If it drops below 6dkh, the "buffer capacity" isnt there anymore, & that enables your ph to drop rapidly as soon as the lights go off.

    This ph drop is caused by the "reduced oxygen" levels at night due to the corals & algae absorbing oxygen, & thus a more carbon dioxide gets released into the water (carbon dioxide causes water to turn acid)
    At day, the photosynthesis of the corals & algae again absorbs the carbon dioxide, & releases oxygen causing the ph to rise...
     
    Last edited: 22 Dec 2013
  5. Visser

    Visser MASA Contributor

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    As for calcium & magnesium... They are linked in a way... They both get absorbed at a constant ratio by hard corals in skeleton building (as is carbonates), but they wont neccesarily all be low if one of them is low...
    There is a fantastic article also by randy holmes that will explain it to you better than any reefer...
    Will post as soon as ive found it...
     
  6. Visser

    Visser MASA Contributor

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  7. Visser

    Visser MASA Contributor

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    If you have any other questions after reading these articles, you welcome to ask, & I will do my best to answer them!
     
  8. Visser

    Visser MASA Contributor

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    Nope, calcium & magnesium doesnt have anything to do with alkalinity or ph (at least not at any significant level) & you can have almost 0 calcium & magnesium, & still have a ph above 8.0 & normal alkalinity...

    Although, if you have a low alk... You will likely see an unstable ph which can drop quite low...

    On the other hand... Calcium & magnesium is linked to a certain extent...
    If you have a low magnesium level... You will struggle to keep calcium levels on par even if you dose high volumes asthe low magnesium limits the calcium levels...

    Please read through the articles, & if you have any other questions... Feel freeto ask, & I will answerthem to the best of my ability...
     
  9. jpaige74

    jpaige74 Thread Starter

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    Wow! You have given me much to research Thank you! :)
     
  10. mandarinman

    mandarinman

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    There is an effective ratio that one should consider. Calcium at a minimum of 420 ppm , magnesium at 3 times calcium as minimum 1260 if cal 420ppm and 1350 if cal at 450ppm. Kh should be calculated in relation to calcium (450 divided by a factor of 43 for sps growth and a factor of 46 for general maintenance). Magnesium can be pushed up to 1650 to rid a tank of algae(takes a while). The reason to test and maintain these levels
    Is to allow corals to survive and have the necessary building blocks to grow
     
    Last edited: 23 Dec 2013
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