Co2 System For Planted Aquarium Diy, Aquarium eBooks

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DIY CO2 System for Planted Aquarium
A Treatise on DIY CO
2
Systems for
Freshwater-Planted Aquaria
by John LeVasseur
This article will attempt to cover all aspects of DIY CO
2
systems used on freshwater-planted
aquaria. Insights into
the needs of aquatic plants in relation to CO
2
, and how this relates to CO
2
injection methods, will be described.
It will examine mechanical designs,
and the biology of
yeast relating to its ability and
conditions by which it produces
carbon dioxide. Formulas for
yeast mixtures and some
details on construction projects will also be
provided.
Contents:
1.
Plants and CO
2
2.
DIY CO
2
Basics
3.
Some examples
of system designs
4.
More than you need
to know about yeast
5.
Guidelines
for Mixtures and Capacities
6.
Construction
Projects
7.
Conclusion
Plants and CO
2
Carbon is
the fundamental element that
all life on this planet
is based. Plants are no
exception.
Since plants have
no way of getting to
their food sources, nutrients have to be
obtained from
their surrounding environment. Plants use
many macro and micronutrients, carbon dioxide
(CO
2
) being one of the primary macronutrients.
In an aquarium
the limiting factors are most
likely
to be (in order): light, CO
2
, micronutrients
(trace elements), and macronutrients. Micro
and
macronutrients are usually supplied in
adequate quantities by fish waste
and the addition of
fertilizers.
Plants
use a process known as
photosynthesis
to produce the carbohydrates they need for life.
Photosynthesis requires light for energy and CO
2
to drive the chemical reactions.
The process of
photosynthesis requires a
specific light energy threshold. In other
words, there is a point where
light has reached a
specific intensity to start photosynthesis.
If the light is not bright
enough,
photosynthesis will not occur.
Beyond that threshold and up
to some high light level,
photosynthesis will run faster and faster. According to
known practice, when
light levels exceed
two
watts per gallon, supplementary CO
2
is required for most
aquariums.
In
our planted aquariums, CO
2
is present without it being added my mechanical
means. Fish
respire CO
2
from their gills. Also in an aerated tank, CO
2
from the atmosphere is
dissolved in the
water.
This effect is known as
atmospheric equilibrium
. In nature though, CO
2
levels are usually
higher
than can be explained by animal respiration or
atmospheric equilibrium, and
aquatic
plants have evolved to this
higher concentration of dissolved CO
2
in water. Carbon dioxide rich
groundwater often feeds
the streams and natural CO
2
concentrations up to several hundred
times atmospheric equilibrium are common.
In general, aquatic plants like to see approximately
a concentration of 10-15ppm of dissolved CO
2
in their environment. CO
2
levels from
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atmospheric equilibrium are generally around 2-3ppm. (ppm stands for
part per million). As you
can see, CO
2
injection is essential
for vigorous plant growth,
and even more so with higher light
levels.
As
far a fish are concerned,
high concentrations, CO
2
can block the respiration of CO
2
from the
fish gills and cause oxygen starvation.
Since the gills depend on a CO
2
concentration differential
between the levels
in the blood and the water to transfer gases, high levels
in the water will
reduce the amount of CO
2
that can be transferred. Although different
references have wildly
varying values
for toxic levels, a concentration of below 30ppm
is definitely safe.
It is a
common misconception that
water can hold
only so much dissolved gas and adding CO
2
will displace oxygen. This is not true.
As a matter of fact, if enough CO
2
and light is present to
enable
vigorous photosynthesis, oxygen levels
can reach 120% of saturation. Even
at night,
when the plants stop using CO
2
and start using oxygen, the oxygen levels will
stay about the
same as a typical non-planted
aquarium. So reports of people having fish at the surface gasping
for air is not necessarily a result of high CO
2
levels, but instead a lack
of oxygen in the water is
probably the
culprit.
The
relationship between light and CO
2
levels is
important. The diagram at the
right explains it
conceptually. At low light and low CO
2
there is not much
energy to play around with for
up or
down-regulation
of the pools of Chlorophyll
or enzymes contained
in the plant. If we
then add a
little more CO
2
to the system the plant
can afford to invest
less energy and resources in CO
2
uptake and that
leaves more energy for
optimizing the light utilization -
Chlorophyll can
be
produced without fatal
consequences for
the energy. Hence, although
we have not raised the
light,
the plant can
now utilize the
available light more
efficiently. Exactly the same explanation
can be
used to explain
why increased
light can stimulate
growth even at very low CO
2
concentrations. With more
light
available, less investment in the
light
utilization system
is
necessary
and the free energy
can be invested
into a more
efficient CO
2
uptake system
so
that the CO
2
, which is present
in
the water, can be
more efficiently
extracted.
Providing macro
and
micronutrients
to plants is easily
done with
commercially available
fertilizers.
It is often a
more
difficult and
expensive task to
provide adequate light over
the
plant aquarium.
Both numerous
fluorescent light and
halide lamps will
produce sufficient light if
supplied with effective reflectors,
but in deep aquaria (more than 20 inches) is
very difficult
to offer
enough light
to small light
demanding
foreground plants.
Based on known experiments, I suggest commencing CO
2
addition before any other action is taken!
I believe that even at very modest light intensities you
will experience a
conspicuous change in plant performance in your aquarium.
The exact amount
CO
2
may always be discussed but concentrations
from 10-15ppm will only improve plant growth.
You will probably
see that plants, which were barely able to
survive before now thrive in the
presence of CO
2
. These conclusions were derived
from work conducted by Ole
Pedersen, Claus
Christensen, and Troels Andersen.
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DIY CO2 System for Planted Aquarium
Basics of DIY CO
2
Systems
Injection of CO
2
into a planted aquarium can be accomplished in several ways. There are
commercial
products available like the tablets
available form Bioplast
and other manufacturers
that use tablets
that fizz like Alka-Seltzer,
and metabolite products like Seachem
Excel. While
these provide carbon sources
for plants, they do not provide
a continuous injection of CO
2
into
the aquarium. Another
method is a pressurized CO
2
system. This is
comprised of a tank of
compressed CO
2
gas, a regulator, and needle valve. While this
is probably the best method
available,
it can be cost prohibitive. A nice compromise
is the DIY
system.
The first step is creating a CO
2
generator, a renewable source of carbon dioxide.
There many
ways to generate carbon dioxide gas,
but the simplest and safest method is
a yeast generator.
Yeast consumes sugar and one
of the byproducts of this is CO
2
. How yeast does this
depends
upon the environment
the yeast and sugar is placed in.
The most common method is to place
yeast
and sugar in a solution with
water. This process
is known as fermentation.
Next, you have to be able to collect the CO
2
and deliver it to the water in the tank. The
yeast/sugar solution
is placed in an airtight container, which
has a fitting that allows a tube
to be
connected. This tube is then
run to meet the water in some way.
At this point
some efficient manner is needed to inject and dissolve the CO
2
gas into the water.
This can be done by directly bubbling the CO
2
gas into the water, passive contact, diffusion, or
forced reaction. These methods will be
discussed in more detail later.
These are the
essential elements of a DIY CO
2
system: A CO
2
generator, tubing, and a water
injection system.
Some examples of system designs
While one
can design a system that is very complex, this might
defeat the cost effectiveness
that warrants a DIY approach. Most of
the designs offered here are done so as examples,
and
are designed with cost savings in mind, while at the same time offering
a high degree of good
engineering practice and efficient
performance. Since yeast generators supply
a limited and
varied quantity of CO
2
gas, it is imperative that the designs used are efficient in their
ability to
deliver and dissolve whatever CO
2
is available over
time.
Basic schematic representation of a well-designed DIY CO
2
system is shown below.
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Yeast Generator
Probably the
cheapest and still the best vessel you can use for
a yeast generator is the two-liter
soda bottle. If you can
find one of those four-liter versions, that is
even better. There are several
factors that make the soda bottle a good
choice. First off, it is designed to hold a
solution of water
with dissolved CO
2
under pressure. This
is important. The pressure that builds up in
a yeast
generator can be substantial. I would venture to say it is not
lethal, but it certainly can make quite
a mess
if it fails and sprays sugar water and yeast all over your
house.
The cap
and how to attach the tubing is another issue that has
created much discussion.
Most of
these caps from soda bottles
are made from polyethylene. Polyethylene does
not readily bond
with most glue. So gluing the tubing in place
is not desirable. Leaks will occur, especially at
the
bond joint. Furthermore, since we're dealing with gasses, the seal
must be airtight. The best all
around
solution is some mechanical means to attach tubing. Some type of
bulkhead fitting is
needed.
Gas Delivery (tubing)
Getting
the gas to the tank water is the next consideration.
Tubing should be selected based upon
several factors. One is
pressure retention, or the ability of tubing to retain
its shape under
pressure. As tubing is put under pressure, it
should not expand in relation to its diameter.
Also the
tubing will need to be inert; meaning not break down
over time due to chemical reaction with the
CO
2
gas internally or the air or water externally.
This pretty much eliminates standard airline
tubing
used for fish tank aeration. Another consideration is
flexibility.
A good
candidate for this application is silicon tubing.
It does not react with CO
2
as quickly, has
good pressure
retention characteristics and is very
flexible. There is also special tubing designed
specifically for carrying CO
2
gas, and I would encourage spending the few extra dollars
needed to
use this. But silicon tubing will
last for several years, and is in keeping with the cost savings
approach DIY
implies.
It
is also important that water is
not allowed to run back down the
line by suction or siphoning.
This problem is
easily remedied with the use of a
check valve
. Many check valves are available
commercially.
Several factors should be considered when selecting one.
I would avoid choosing
one made from metals.
The caustic nature of CO
2
gas, the high water vapor content of the gas
(which usually contain carbonic acid), will cause a metal check valve to fail.
Therefore it is
important
to choose a plastic valve
or one designed specifically for CO
2
applications. In addition,
for the same reasons,
I recommend avoiding the use
of any metal components in the entire
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DIY CO2 System for Planted Aquarium
system. In pressurized tank systems, there
is generally no liquids, or solids for that
matter, to foul
or corrode
metal components. So the use of metal
components is common in these
systems. The
same should not be
assumed on a yeast based DIY
system.
Getting the gas dissolved in the water
This
is a topic that has received much attention on
message boards, mailing list servers, and
newsgroups over the years. And I
think rightfully so! Many methods
have been described on what
the best way to dissolve the CO
2
gas into the tank water.
This is the critical point in determining
the effectiveness of a
DIY system and the reason why many feel that
their experience with DIY
systems was a bad one. Since the amount of CO
2
available in a yeast system is limited
by
biological production, it is important to get most,
if not all, the CO
2
produced dissolved into the
water. Skimp here, and you have wasted your
time, not to mention CO
2
gas.
The
simplest, and least effective, method is to
run the tube into the tank and simply let
the gas
bubble into the
tank, or through an air stone.
I do not recommend this method at all.
Since most of
the CO
2
gas simply rises to the surface and
is lost.
Next,
many have suggested placing this tube at the
inlet of a canister filter and allowing the
impeller to munch
up the gas. While it is effective in dissolving
the gas, I do not like this method
either, for two
reasons. First, the CO
2
bubbles can produce cavitations of
the impellor, which
could
cause it to vibrate, making noise and
possibly damage the mechanism.
Second, some of
the components
in the impellor use rubber fittings,
which could be broken down over time by
the
high concentrations of CO
2
gas and carbonic acids present.
A
better but slower method is the use of what is
called a CO
2
bell. Simply put, this is a
hemispherical shaped
vessel of some kind, inverted
and the CO
2
is allowed to fill up inside. The contact
area of the gas
is increased and passive
diffusion
of the gas is increased.
The drawback of this is if
the surface area is not
high enough, so that
diffusion rate exceeds
gas production, the bell will
fill with gas and
any additional bubbles will run out
the side and travel
up to the surface and be lost.
While this is a draw back, many aqaurists
have
have had reasonable sucess using this
method of
gas diffusion. These are
also very simple to
construct. Many have been constructed
from
cutting off the tops of one-liter
soda bottles, petri
dishes,
cups, or any hemisphercal shaped object.
I
would recommend using a
material or object that is
transparent, to allow
for easy viewing.
Another
method is a diffuser. Two versions of diffusers exist.
One is device that increases the
time the bubble is
in contact with the water. Usually by
presenting the bubble
with a long spiral course
it has to travel. In the image to the right is
one
example of this type of spiral
diffusion method, the Econo Aqualine
500
available from AquaBotanic, and
others. The manufacturer claims,
"The
special construction allows a very high CO
2
diffusion rate and automatically
removes
any false gasses. The reactor is
sufficient for an aquarium up to
125
Gallons". This unit is mounted
on the inside of the aquarium.
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