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Re: CO2 and anabantoids

Date: Tue, 26 Oct 1999 14:23:31 -0600
From: Shannon Wheeler

> You mean, 'they CAN breath air in ADDITION to dissolved
> O2...'. Right?

In some cases it seems they *must* breathe atmospheric air *in addition to*
the oxygen dissolved within the water. Even informal studies, such as that
printed in a recent AFM, confirm that Bettas, for example, "drown" when
denied access to surface air supplies...

Date: Mon, 25 Oct 1999 18:48:11 -0400
From: Dinyar Lalkaka

> the notion that co2 escapes from the water and then
> "loads" the air above for a significant period of time is
> silly. if that were the case, then by the law of partial
> pressures, recently elucidated on this list, part of it
> would dissolve back into the water and the tank co2
> level would be higher than ambient room air.

Date: Tue, 26 Oct 1999 10:23:35 +0000
From: Jan Fidrmuc

> >Why would this be silly. If there is a continuous supply
> >of CO2, it may accumulate above the water surface even
> >if part of it dissolves back into the water. The worrying
> >thing is that CO2 is heavier than regular air. Hence, with
> >a tightly fitting cover, there may be an oxygen-free, CO2
> >loaded layer above the water surface. If the cover does
> >not fit tightly, this problem is less likely to arise because
> >of air circulation.

Date: Tue, 26 Oct 1999 19:26:50 -0400
From: Dinyar Lalkaka

> It would have to be very tightly fitting indeed.

> ...lots of fish, eg, many catfish families, breath atmospheric
> air. With an air tight cover, you'd have problems with or
> without CO2.

Date: Tue, 26 Oct 1999 18:32:35 -0500
From: Larry Jones

> >>..it would have to be a really tight lid. Throw a piece of
> >>down in the air and see if it falls straight down. It should
> >>if there are no air currents. Now just imagine a piece of
> >>down as small as a CO2 molecule.

Date: Tue, 26 Oct 1999 19:27:15 -0500 (CDT)
From: Ivan Trail

> ** One question first:  Why would anyone put a tightly
> ** sealed cover over their tank?  I personally have never
> ** seen a pond or lake in the wild covered in this manner.
> ** Maybe there is a reason I don't know of.  If so please
> ** tell me.

The "traditional" approach to Dutch-style aquatic gardens involves, among
other considerations:

Biasing the bioload in favor of the plants. Unlike many American-influenced
designs, the Dutch aquarium is established for the benefit of the plants,
not the fish, so conditions are set to provide the best environment for
plant growth. Fish are usually added for two reasons - a decorative offset
and to provide macro- and micro-elements common to their waste on a
continuing basis.

Low circulatory "turnover" rates. Again, unlike American-influenced tanks,
the Dutch aquaria have no need for massive filtration rates or turnovers
involving "quantum leaps" in the number of tank volumes per hour. A very
slow - often only a single tank volume - turnover rate is set merely to
provide circulation of the nutrients among the plants. This raises the most
concern for the fish at night, when the plants are respiring far more than

CO2 enrichment. Fertilization and high light levels need to be compensated
for by eliminating CO2 as the limiting factor - hence the need for
"supplementation". And face it, folks - the idea of injecting CO2 in the
first place is to achieve dissolution levels "higher than ambient air" will
allow. But CO2 costs money - whether it be the outright cost of bottles,
regulators, dissipators and refills or the implied labor and supplies used
in DIY yeast generators. The "very tightly fitting lid" is used with the
expressed intent of trapping outgassed CO2 *at the water's surface* and
increasing *its* partial pressure in order to reduce the amount of CO2 that
has to be injected directly - a move based strictly on "economy".

Ivan Trail continues with:

> ** Now, back to my theory.  The law of partial pressures
> ** states in a nutshell, "The gasses in a given container
> ** will be evenly distributed through out."  This is why there
> ** is no cloud around a smoker.  The smoke seeks to
> ** make a balance with all other gasses in the room.   No
> ** fog around your face on a cold day.  No green cloud of
> ** foul aromatic esthers aruond a person who has just
> ** eaten Uncle Bob's Flamin Hot Chili.

OK, now that *that's* established, how about extending it to the size of the
container *in question*? Would you want to be travelling down the road in a
closed-in truck cab, no ventilation and the same smoker - especially if
you've just attempted to quit yourself? Would the "green cloud" be more
noticeable if you were trapped in a locked closet with that person?

> ** We know that in a tank with fish, enough O2 exists to
> ** support the life of the fish.  The evidence is obvious.
> **
> ** So, if the CO2 dissipates out of the water, then so
> ** should the O2 and whatever other gasses are present
> ** in the water.  thus the layer above the water in a tightly
> ** covered tank should be made upof the same gasses
> ** in the same proportions as in the water, all equaly mixed.
> **
> ** now that only leaves to assume that since the gasses
> ** in the water are able to support life, then the
> ** accumulated gasses will support life also.

This assumption is invalidated as soon as you apply a tight-fitting top to a
CO2 injected system. The enclosed airspace becomes *positively pressurized*,
with the additional pressure originating from the excess CO2 delivered to
the system. There is *no* mixing with atmospheric air because of the
pressurization. Nor are the partial pressures of the various gasses held to
the same constant as within the water simply because the air mix is
continually expelled in favor of the excess CO2 that rises to the surface.
It has no choice because it doesn't *completely* dissolve in the water,
despite your best efforts - particularly with yeast generator methods.

When Ole Larsen first posed the question on the *aquaria newsgroups, I
couldn't provide him with a definitive answer based merely on experience.
The tanks I have with CO2 injection contain several forms of catfish, which
seem to be unaffected by the situation. My assumption here is because of the
difference in *how* the "gulped" air is assimilated - rather than directly
as with the labyrinth organ, the oxygen is absorbed by the digestive tract,
where it is most likely mixed with all manner of other elements and the
separation and absorption process is geared more toward that type of
internal "environment".

Such is not the case with Anabantids. But I don't have the experience with
them in an enriched tank. The 'bantid tanks I keep with tops on them use
air-driven sponges - a source more for oxygen than CO2 - and the tops are
there to maintain a warm, humid environment at the water's surface because
they're breeding and grow-out tanks.

Since my breeding program is beginning to develop some real "keepers",
though, I find myself in a position where I might easily be maintaining some
of the fish in the type of environment in question. Where this list is
concerned, I've only been a "lurker", as my planted tank experience isn't as
advanced as my fish maintenance. But here is a question in which I'm
*keenly* interested, so I might just jump in again to keep the discussion
headed in a more productive direction. I hope no one minds too greatly...


David A. Youngker
nestor10 at mindspring_com