Re: Low pH nitrification THE ANSWER?

[WndrKdnomo@aol.com]

In a message dated 10/21/98 5:09:54 AM, IDMiamiBob@aol.com writes:

<< Not all the ammonia converts to
NH4+.  that which is still NH3 would get metabolized.  As soon as it is gone,
NH4+ ions would convert back to NH3, in an attempt to achieve "stasis", >>

You are absolutely correct, in that there is an "equilibrium" between the
ionized and unionized forms of ammonia.  Basically, as you indicate, this
means that at a given pH a certain percentage will be in each form, NH4+ or
NH3.  If you remove some of the NH4+, some of the NH3 will be ionized to
maintain the equilibrium state.  This is true at ANY pH.  However, at highly
acidic pH values, the percentage of unionized ammonia that is "bioavailable,"
if you will, is very, very low.  (My old biochem books are all packed up, or
I'd look it up).  Even if the ammonia reducing bacterium (and the exact cast
of characters in aquatic environments is still uncertain, see earlier
postings) is still alive and active at low pH, the conversion of ammonia to
nitrite would be very much slower than at neutral pH.  At the same time, the
fish are producing ammonia/ammonium at the same rate, regardless of pH.  Thus,
you wind up in the same practical situation as if NO conversion was taking
place.  That is, even if you have some nitrate accumulation as the result of
Nitrogen Cycle activity, you may ALSO have a high concentration (relatively
speaking) of ammonium ions.  In practical terms, this still means no large
water changes in highly acidic aquariums if your new water has an appreciably
higher pH.  This is only common sense, as you don't want to expose your fish
to large pH swings anyway.
     As a further note, someone was wondering how a low pH tank could function
and not "crash" if no Nitrogen Cycle activity was occurring, I will repeat
what was said earlier. The ionized ammonium ion (NH4+) does not pass through
cell membranes (read "gills") and therefore is not take up by organisms, and
is not toxic to our fish. Therefore, it does not really matter if nitrate or
ammonium accumulates in our low pH tanks, as long as correct tank maintenance
procedures are followed.
I hope you're all taking notes, there's  a quiz next Wednesday. ;)~
      Any scientifically curious people out there? High school seniors/college
undergrads. looking for a term paper topic?  Take a sponge filter out of an
established low pH tank, rinse thoroughly in tank water, and place in a tank
with R/O water buffered to a pH of, say, 5.0 (Multiple tanks with varying pH
values, and a control at pH 7.0 would be best, of course).  Take ammonia,
nitrite, and nitrate readings (there will be some contamination from the
sponge filter, you need to know what your baseline is).  Then add a known
amount of pure ammonia.  Take your readings immediately after adding, and at
regular intervals thereafter.  Various results might occur:
1) ammonium is converted to nitrite/nitrate at or near the speed of the
control
2) ammonium is converted to nitrite/nitrate but slower than control
3) ammonium is not converted to any significant extent.
 You would need to be ABSOULUTELY certain that your test reagents were
accurate at low pH values, not all are.
Depending on which result occured a much clearer picture would emerge of the
microbiology occuring (or not) in our tanks.
    I hope this helps for those of you interested (anyone?).
Jeff							PS.  In terms of water changes, those who make LARGE water changes
to stimulate spawning ("Rainy Season") will be OK in most conceivable
instances, even if the new water is only slightly acidic.


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