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RE: Determining CO2 Concentrations in Natural Waters

"You're a Floridian - ever go looking for Elosoma
(dwarf sunfish)?"

Are you crazy man! I am from Brooklyn and New Jersey.
I do however like the Florida weather especialy since
it makes it easier for me to keep my fish. GO METS,
the sad Kincks.


--- "David A. Youngker" <nestor10@mindspring.com>
> > From: David A. Youngker
> > Sent: Monday, January 28, 2002 6:43 PM
> > Speaking of concentration, mine's beginning to
> fade right
> > about now - been _very_ sick the last few days
> (sorry I
> > was off-line, Teresa). And as this is rather
> detailed, I'll
> > pause here momentarily to entertain any questions
> up
> > to this point. We'll continue once this is
> established.
> Up for a short break while my sweat-soaked bedding
> is changed out - a "water
> change" for me ;-)
> Back to David's arguments:
> > External factors certainly play a point in this
> > but to say that CO2 levels are "entirely"
> determined
> > by external factors is just not a scientifically
> sound
> > principal.
> Not exactly certain of the point you're trying to
> make here. The factors
> that influence the pH/KH/CO2 relationship are
> definitely external to the
> solution involved, as they are products of the
> varying topology and geology
> the water encounters along its flow. The topology
> affects the contact time
> while the geology provides the range of compounds to
> which the water is
> exposed.
> Ever take a look at the calculations in an Ecology
> text or site? They
> usually provide some kind of qualifying disclaimer,
> such as "assume there is
> no contact with carbonate-based compounds", "does
> not apply where the water
> is in contact with carbonates", etc.. That's so as
> to provide an
> instantaneous "snapshot" of the _current state_ of
> the water, as any
> acid-bearing solution will cause the further
> dissolution of carbonates,
> affecting the calculations. And any water that has
> carbon dioxide dissolved
> into it (essentially anything that contacts the
> atmosphere) contains an
> acid. So we make the current situation "static" in
> order to limit the
> calculations to algebra and not have to deal with
> calculus (which _does_
> describe the results of changes to a dynamic
> system).
> Then there are sources of carbon dioxide to consider
> as well. Carbon dioxide
> is the result of aerobic biological activity, so any
> water containing
> sufficient nutrients - especially carbon-bearing
> ones - provide the food for
> organic activity at the bacterial level if nothing
> else. Flora and fauna
> respiration add to the overall content. Underground
> activities can be a rich
> source, as the pH around a lot of springs will tell
> you.
> > However I am not advocating adding CO2 to a system
> with
> > sufficient CO2 present as can be found in a system
> with
> > a low KH and pH. All my tanks have a 0 KH and I
> don!&t
> > have any so-called pH bounce or crash. I just
> change my
> > water regularly and dispose of the organic
> compounds that
> > would begin to leech acids over time.
> The pH "bounce" everyone mentions is normally a high
> KH phenomenon
> associated with trying to change the chemical
> parameters to the low end -
> the pH rarely "bounces" when adding the buffering
> agent itself. It is caused
> by the rebalancing of the carbonic- to- bicarbonate
> ratios of the
> equilibrium.
> When we add a mineral acid to high KH water, the
> hydrogen concentration
> naturally rises along with the rather _immediate_
> dissolution of the acid.
> The shift from carbonic to bicarbonates (or vice-
> versa) takes considerably
> more time along the same scale. Dumping a lot of
> hydrogen into the system is
> like hitting a big pothole with your car- an
> immediate, large input is
> dissipated across time through the action of the
> shock absorber. This gives
> the absorber a chance to dissipate the energy
> through other mechanisms
> rather than providing a "straight line jolt".
> With that in mind, a large influx of hydrogen will
> initially show as a large
> downward shift in pH because of the number of free
> hydrogen ions present -
> the concentration has increased. But as the
> bicarbonates are driven into
> absorbing hydrogen to become carbonic acid, hydrogen
> is removed from the
> solution and into the solute. Now the pH shows as
> low because there is a
> disproportionate amount of carbon dioxide in the
> water, directly affecting
> the carbonic- to- bicarbonate ratio. Since the CO2
> can usually outgas
> quicker than it is dissolved, the excess bleeds off
> to the atmosphere (a
> carbon dioxide sink). The result strikes a new
> balance in relation to
> atmospheric levels of CO2 and the now lowered
> bicarbonate population.
> A pH "crash" occurs when there is no more buffer to
> dissipate the influx of
> hydrogen through out gassing. In such a case, the pH
> is tied directly to the
> amount of hydrogen added to the system and we have a
> "straight count
> population". In other words, a direct influence on
> pH.
> As to why your tanks don't "crash" at such low pH/KH
> combinations, consider
> some of the "organic compounds that would begin to
> leech acids over time".
> If you filter with peat or Oak leaves, one of those
> "organic compounds" is
> tannic acid. Hmmm...tannic acid. Acid. Complete with
> transferable hydronium.
> But tannic acid is a much weaker acid that those
> produced by nitrification,
> and is a pretty weak buffer. The consistent water
> changes will replenish the
> buffer while depleting the nitrates, keeping
> everything on a pretty even
> keel.
> > Most importantly the plants themselves will do a
> > great job of maintaining you pH. A healthy tank
> > with good plant growth will have a higher pH. Why?
> > Because the plants are using up the CO2 and thus
> > there is less available to make carbonic acid.
> This depends on a few more of those "external
> factors".
> Light intensity is, of course, paramount. Light
> energy is the initial
> impetus to the system, determining the metabolic
> rates of the plants. More
> light or more plants increases the demand for
> carbon, and it does indeed
> remove CO2 from the system. However, in a
> circulating body of water as small
> as a tank, the carbon dioxide can often be
> maintained at atmospheric levels
> just through contact. But the key here is that it
> _is_ replaced, although
> the replenishment may not happen with sufficient
> speed to keep up with
> depletion. Then your pH may indeed go _very_ high as
> the plants start
> cracking bicarbonates to obtain CO2.
> But since light energy _is_ the key, that means
> everything's tied to the
> *diurnal cycle*. The plants will drain the CO2
> during the day, and the
> atmosphere and respiration will replenish it during
> the night. A 12-hour
> "high-low" doesn't sound very stable to me,
> especially if it's fluctuating
> by a couple of points - which is distinctly
> possible. Carbon dioxide
> injection keeps the depletion and replenishment
> rates fairly consistent
> across 24 hours.
> > I have yet to see any natural bodies of water with
=== message truncated ===

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