RE: Determining CO2 Concentrations in Natural Waters

[David Sanchez <barbax2@yahoo.com>]

"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,
YANKEES, ISLANDERS, DEVILS, GIANTS, JETS, and yes even
the sad Kincks.

THE DAVE



--- "David A. Youngker" <nestor10@mindspring.com>
wrote:
> > 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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