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Homework Help: Nitrate and pH in a Fishlessly-cycled Aquarium

  1. Jun 18, 2011 #1
    1. The problem statement, all variables and given/known data

    Prior to introducing livestock, a fishkeeper may establish colonies of nitrosifying and nitrifying bacteria by repeatedly inoculating an aquarium with a solution of ammonia (to simulate the presence of fish). At the end of the process there is a high concentration of nitrate in the water - typically of the order of 80mg/l.

    May such a concentration of nitrate lower pH?

    2. Relevant equations

    [none understood]

    3. The attempt at a solution

    And anyway, what kind(s) of nitrate is it? Cations can come only from the virgin water (usually tapwater) in which there is typically a preponderance of calcium and magnesium. Is calcium nitrate more likely than magnesium nitrate? I have read that the former's pH is around 4 or 5 ; while the latter's is around neutral. So if calcium nitrate forms there'll be a heap of extra H+ ions around ...

    ... which is fine so long as there's sufficient buffer (in the form of bicarbonate) to soak them up. If not, then presumably high nitrate in low-buffered water would indeed tend to acidify? Would nitric acid form?

    Or am I on the wrong track altogether?
  2. jcsd
  3. Jun 19, 2011 #2


    User Avatar

    Staff: Mentor

    The only thing I can think of is that oxidation of ammonia can acidify the solution:

    NH3 + 2O2 -> HNO3 + H2O

    You don't produce calcium or magnesium nitrate, these cations were in water and they are still there, nothing have changed.
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