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Safe Guard Your Koi - Control Carbon
Dioxide Spikes

Algae Bloom Causes Carbon Dioxide Levels
To Rise At Night

Carbon Dioxide (CO2) And Oxygen (O2)
work hand in hand in a garden pond. As
oxygen levels in the pond water
increase, the level of carbon dioxide
decreases and vice versa. This is a
natural process. Oxygen levels are at
their lowest at dawn, due to the
processes taking place in your pond over
night. During the day as sunlight
appears the level of oxygen rises,
peaking when the sun sets. After sunset
the carbon dioxide which is at its
lowest at this time of day starts to
rise, peaking just before sunrise. It is
important to not let carbon dioxide
spikes, caused by green algae blooms
from killing your pond fish. The best
way to do this is to use a UV clarifier
or a UV sterilizer.

How Does Carbon Dioxide Get Into My
Pond?

Carbon dioxide is produced by aquatic
pond life such as fish, snails, algae
and aquatic plants through respiration
(breathing). It is also produced as a
result of rotting organic matter on the
pond floor, including leaves, uneaten
fish food and decaying algae blooms.

Carbon Dioxide Spikes Cause Fish
Fatalities

Here is a question for those of you who
have a fish pond! Have you ever woke up
in the morning and found several of your
pond fish dead? You probably stood there
scratching your head, wondering why?
There are two likely causes:

* A predatory animal such as a bird or a
cat has physically killed the fish. The
tell tale signs should be fairly
obvious; damage to the body or head, for
example.

* If your pond suffers from heavy algae
blooms then the most likely cause is
suffocation, through lack of oxygen. The
pond water will need to have contained
high levels of carbon dioxide and
extremely low levels of oxygen for this
to have happened.

If the cause of the deaths is due to the
high level of green algae blooms then
the best way to remedy this situation
quickly is to install a UV clarifier or
UV sterilizer, as these units will
usually manage to get the algae bloom
under control within about 5 days. With
continuous use a UVC light will keep
your pond water free from algae bloom.
Please note however that a UV will not
remove blanket weed or other filamentous
string algae types.

What Is Photosynthesis?

Planktonic algae are a form of
microscopic plant life that consumes
carbon dioxide, during the day and
reverts to using oxygen at night time.
All plants carry out a process known as
photosynthesis. Photosynthesis uses the
energy of the sun to convert inorganic
carbon (gained from CO2 dissolved in the
water) into carbonic acid (H2CO3).
During sunlight hours plants and algae
absorb carbon dioxide from the pond
water, causing the level of carbonic
acid to fall. This causes the pond water
to become more alkaline i.e. the pH
level increases.

Carbon Dioxide Problems Are Lower In
Winter

Oxygen levels in pond water are at their
highest during the colder fall and
winter months when there is
significantly less biological activity
taking place within your garden pond.
There is an overall reduction in the
level of nutrients (nitrates and
phosphorous) present in the water. This
is mainly due to the plant life and pond
life producing less waste; the plants
have stopped growing and pond fish feed
less. There is also less sunlight
resulting in algae populations
diminishing. For this reason the overall
fluctuations between oxygen and carbon
dioxide levels during the day and at
night will be significantly less. The
chances of Koi and goldfish deaths are
significantly reduced.

It is also much easier for atmospheric
oxygen to dissolve in cold water than it
is for it to dissolve in warmer water.
In addition cold water is able to hold
more oxygen than warm water. Have you
ever noticed pond fish gulping for air
at the pond surface on hot, sunny days?
This is the reason why.

How Carbon Dioxide Affects Pond pH
Levels

The ideal pH for garden pond water is
between a pH of 7.5 to a pH of 9. Carbon
Dioxide dissolves in water to produce
carbonic acid (H2CO3), which has a pH of
less than 7. As a result the pond pH
will drop and become more acidic as the
carbon dioxide levels increase in line
with the increased respiration from
aquatic life. This is exactly what
happens during the night in your pond.
During the day the opposite is true,
where photosynthesis boosts the increase
in oxygen, causing the pH level to rise
and become more alkaline. It is when the
pH level drops and becomes more acidic
that the potential for carbon dioxide
problems increase.

What is Pond pH?

The pH scale which ranges from 0 through
to 14 signifies whether or not the pond
water is acidic (below pH7) or alkaline
(above ph7). A pH of 7 is neutral. The
higher the number of free hydrogen ions
(H+), the more acidic the water is. A
neutral pH means that the number of
positive hydrogen ions (H+) are the same
as the number of hydroxyl ions (OH-).

Aeration Increases Oxygen Levels and
Reduces Carbon Dioxide

Garden ponds can never have too much
oxygen. A well aerated garden pond will
suffer considerably less from the
catastrophic effects of high carbon
dioxide levels, such as fish fatalities.
Using a waterfall, water feature or pond
air pump will add valuable oxygen to the
pond environment, which will push the
pond pH up and remove carbon dioxide
from the pond water.

Pond Buffers Increase Pond pH Levels

A buffer is any substance that reacts
with an excess of hydrogen ions (H+).
The most commonly used buffer is Calcium
Carbonate (CaCO3) which is frequently
used in garden ponds to prevent the pH
from becoming acidic. It is a good idea
to add a buffer to your pond filter to
prevent fluctuations in pH levels.

CO2 + H2O ---> H2CO3 ---> H+ + HCO3-

In the above example, carbon dioxide +
water form carbonic acid. This
disassociates into two ions; including a
free hydrogen (H+) ion.

CaCO3 + H+ + HCO3- ---> Ca (HCO3)2

In the above example, a buffer such as
calcium carbonate (CaCO3) bonds with the
free hydrogen ion, to form Calcium
Bicarbonate Ca (HCO3)2.

As long as you have calcium carbonate in
your pond filter, your pond water will
be protected against swings in pH. A
buffer will also work in reverse;
releasing hydrogen ions back into the
water should the water become
excessively alkaline.

A pond should be a real enjoyment and
will be if you are aware of what is
actually happening below the surface. My
advice to you would be to ensure that
you use a branded biological pond
filter, a reliable energy efficient pond
pump and a UVC sterilizer or UVC
clarifier. Ideally you should add
additional oxygen into the pond water;
water falls and pond air pumps are the
best way to do this.

Remember to ensure that you regularly
check your pond water for ammonia,
nitrite, pH, total Alkalinity and
possibly hardness using a suitable pond
test kit to quickly identify any
potential problems.

After sunset the carbon dioxide which is at its lowest at
this time of day starts to rise, peaking just before
sunrise. It is important to not let carbon dioxide spikes,
caused by green algae blooms from killing your pond fish.
The best way to do this is to use a UV clarifier or a UV
sterilizer.

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