Carbon
dioxide (co2) supplementation is very beneficial for the planted
aquarium. Aquarium plants quickly use up the co2 found in non-supplemented
tanks. Adding more co2 than would naturally be found in an aquarium
accomplishes two things. It gives plants a source of carbon and
lets the tank owner control the pH.
In an aquarium where additional co2 is not introduced, one might
expect to find roughly around 5 parts per million (ppm). Many easier
aquarium plants will do fine with that amount but do a lot better
with a higher level of 25-40 ppm. Some plants can't be grown at
all without it. How do you know how much is present in your water?
If you know two of these three things—co2 level, carbonate
hardness (KH), and pH—you can figure out the other. Charts
and calculators are easily available that let you figure out the
third value that is unknown. The easiest way to figure out the pH
is to use an electronic monitor. Milwaukee, Hannah Instruments,
and Pinpoint make reliable and affordable units that are easily
available. Using them is much easier than trying to compare a sample
to a paper card or even water samples dyed to match different pH
values.
The level of co2 in an aquarium depends on the quantity of co2 introduced
and on two other factors. One is the KH of the aquarium water. Carbonates
act as a buffer and act against a drop in pH. A high KH will mean
that in order to achieve the desired pH, a overly high level of
co2 has to be introduced. A carbonate hardness that is too low is
more of a problem. If it is below 4 dKH, adding co2 may result in
a dangerous pH drop. A KH of 4-6 dKH and a pH of 6.5 to 6.8 are
optimum for most planted tanks.
The other factor having to do with how much co2 is present is the
degree of surface disturbance of the water. There should not be
any. Airstones and splashy filters simply drive out any co2 that
is added or already in the system. If you use a power filter and
it has a biowheel, remove the wheel.
Under no circumstances should the co2 level be allowed to go over
40 ppm. Fish can survive levels of up to about 90ppm for a time,
but shrimp cannot tolerate that much carbon dioxide. Co2 levels
will be highest in the evening after much of it is used up by the
plants and lowest in the morning since they do not use it at night.
With good plant growth, plenty of oxygen is created and both plants
and fish will have more than enough to last them through the night.
It is hardly ever necessary to run an airstone or turn off the co2
while the lights are off and can actually be a detriment, as larger
pH swings occur as a result of those practices than would otherwise
occur.
How can carbon dioxide be introduced? There are several options.
For tanks 30 gallons and under in size, the aquatic gardener may
make use of what is commonly known as DIY co2. Yeast and sugar are
combined in a plastic container with an airline running to where
the co2 will be introduced. Do not use glass! In the very unlikely
event of an accident, dealing with shards of glass is definitely
not a good thing. Take an empty 2 liter bottle or Gatorade container
and remove the cap. Drill or melt a hole (with a hot nail) in the
lid that will be big enough for a short piece of rigid airline tubing
to penetrate. Seal this with aquarium sealant. When it has cured,
fill the container to near the top with warm but not hot tap water.
Add 2 cups of sugar and a teaspoon of yeast from yeast packets.
Those amounts are not set in stone, and can be varied according
to need. A piece of silicone airline tubing is then attached to
the glued in rigid airline protruding from the top and run to where
the co2 will be introduced (more on this later). A one-way check
valve will prevent any aquarium water from siphoning back into the
bottle when it is changed. It is preferable to situate the unit
above the aquarium for that reason.
Initially, co2 production may be quite vigorous. After a week or
two, production starts to slow down when either the yeast runs out
of food (the sugar) or is killed by the alcohol it produces as a
byproduct of the fermentation. At that time, simply dump the mixture
and start over.
As mentioned above, this method of co2 introduction is best suited
for smaller tanks. It would simply take too many bottles to supply
the co2 needed for a larger tank. For example, a 30 gallon tank
with good light requires two to three bottles running at the same
time. After a while, remixing the yeast and sugar mixture becomes
tiresome. Yeast co2 is a good introduction to carbon dioxide supplementation
and its positive effects, but there is a much easier way to accomplish
the same goal.
As many plant growers gain experience and grow tired of yeast co2,
they usually turn to a compressed gas system. A basic system is
composed of the following parts. A regulator attached directly to
the bottle regulates the outgoing pressure, which is shown on the
right of its two gauges (the other shows how much co2 is left in
the tank). Connected to the regulator or inline with the tubing
is a needle valve, which has a small dial used to control the particular
bubble rate. An optional bubble counting device may be used after
the needle valve as a way to quickly see that everything is working
properly, but should not be used alone as a means of determining
how much co2 to add. As with yeast co2, a check valve is used, this
time to prevent water from flowing back into the needle valve.
For approximately $150 to $175, a simple system with a 5 pound bottle
can be constructed. After that, refilling the bottle or swapping
for a new one at a beverage distributor or welding supply store
costs $6 to $10. Bottles up to 20 pounds are a little more expensive
but last a lot longer. The co2 refills actually cost less than all
the yeast and sugar it would take to operate a yeast system.
A pH controller and magnetic solenoid valve can be used to moderate
the flow of co2 and consequently the pH so that it never varies
at all, but are hardly necessary, as the daily pH swing of .15 to
.2 pH units seen with simpler systems is normal and nothing to worry
about. Additionally, adding those two pieces of equipment adds around
$300 to the system cost. If you have the money and like gadgets,
go for it. Otherwise, save your money.
Although the initial investment is higher, pressurized systems are
far superior to yeast driven ones. The co2 level is constant and
does not rise and fall very much as long as the carbonate hardness
is maintained. A five pound bottle keeps a 30 gallon tank supplied
for about 4 or 5 months. During that time, occasional pH checks
are all that is needed. That's all. It certainly makes running the
tank a lot easier.
A few liquid carbon dioxide replacement supplements are available
from various manufacturers. Seachem's Flourish Excel is an organic
carbon based formula that can work well for lower light tanks. It
does not seem to work as well in higher light tanks. I do not have
experience with any similar products, but I can say that some of
their advertisements imply that normal plant feeding and nutrition
is not necessary when using them. That cannot be the case.
Where does the carbon dioxide from the yeast or pressurized system
go? As with the system itself, there are several options. The co2
dissolves into the water on its own but does need as much contact
time as possible. One way is to simply run it into the filter. Canister
filters are best for this purpose. As long as too much isn't fed
into them, Eheim and Marineland filters work fine. Fluvals (at least
the older 03 series) are not as good at evacuating gasses and can
quickly lock up. The former two do "burp" from time to
time, but as long as the filter flow is not restricted somehow (such
as a kinked hose), everything should be fine. A variety of internal
filters and even power filters also work for co2 introduction, but
not quite as well.
A second option is a reactor. Co2 is introduced into the bottom
of the chamber against opposing water flow and often bioballs that
serve to trap the bubbles so they have more time to dissolve. Water
flow can be from a canister filter (where the reactor is plumbed
inline) or from a powerhead or pump.
Co2 may be directed right into a powerhead, although this method
is less efficient because many of the tiny bubbles produced make
it to the surface before they can dissolve.
Another method of introduction is through what is known as a diffusor.
Co2 is forced through a ceramic disk as a fine mist that is blown
around the tank by the current. The disk should be placed as low
in the water column as possible to give the bubbles as mush contact
time as possible. The disk needs to be cleaned on a regular basis
to remove algae and debris build up.
A few words of safety about co2 are necessary. As mentioned above,
do not let the carbonate hardness fall below 4 dKH. This is especially
important with pressurized systems since many regulators will allow
a higher amount of co2 to flow out as they get close to empty. Without
a needle valve to help slow it down, the result can be a large pH
crash and the death of the tank's inhabitants. Do not ever go without
one! Keep an eye on the regulator gauge that shows how much co2
is left. Also, be sure to strap or chain the bottle to a sturdy
structure or wall to prevent the possibility of it falling over.
Please keep in mind that as long as these rules are followed, there
should be nothing to worry about.
Co2 supplementation is often the difference between a few struggling
plants and a flourishing underwater garden. It is most definitely
worth the time and money to create a system for its introduction.
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