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| Algae
and Your Pond |
Algae
Growth (Photosynthesis)
Koi ponds are usually closed recirculating aquatic systems,
meaning that these systems, unlike natural ponds with streams
flowing through them, lack a fresh water flow-through source.
Rather, closed recirculating aquatic systems rely on filtration
to purify and reoxygenate their water. Outdoor ponds that are
closed systems are subject to seasonal algae blooms and attached
filamentous algae growth due to nutrient and carbon dioxide
buildup. Increased levels of nutrients and carbon dioxide create
the potential for a healthy algae population. Pigments
(chlorophyll, fucoxanthin and carotenoids) in the algae absorb
light energy and use it to convert carbon dioxide and nutrients
into new cell biomass through photosynthesis. The primary
nutrients of concern are nitrogen and phosphorus. Nitrogen
is a byproduct of decomposed fish waste, uneaten fish food
and accumulated sludge in the bottom of the pond. Page six
describes the nitrification process, the conversion of ammonia
to nitrite to nitrate – which is nitrogen.
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Planktonic Algae
Planktonic algae are waterborne single-cell algae, most commonly
referred to as Green Water. Planktonic algae (algae bloom) usually
occurs as a result of increased levels of nutrients and carbon
dioxide in pond water, combined with the energy of sunlight.
Planktonic algae can be controlled with aquatic plants, shade,
ultraviolet sterilization or chemical methods. Using aquatic
plants as an algae control requires that a specific number of
mature plants are added to the pond to compete with the algae
for the available nutrients and carbon dioxide. Shade is available
only if foliage or a shelter inhibits the pond’s exposure
to sunlight. Chemical treatments can be successful, but they
can be expensive, temporary, and potentially harmful to plants
and fish.
The most effective method of Planktonic algae
control is ultraviolet sterilization.
The
many advantages of UV sterilization make it a very attractive
option for algae control. First, it is a physical treatment,
so it does not change the water chemistry of the pond. Second,
it is very easy to install. Third, the treatment takes place
outside the pond, away from the fish and plants.
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Filamentous
Algae
Attached filamentous algae can be seen growing on the rocks
of a waterfall or on the sides of the pond. The growth of filamentous
algae results from high levels of nutrients, carbon dioxide,
and the catalyst, the Sun’s energy. Methods of controlling
filamentous algae include increased shade, reducing the frequency
of fish feedings, practical water changes, and the use of chemicals
or plecostomus (algae-eating fish) during the summer months.
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Algae Isn’t Bad, Is It?
Algae can be either beneficial or detrimental to a pond, depending
on the owner’s viewpoint. Algae provide nutrients for
newly hatched fry, and indirectly act as a color enhancer. As
algae grow in a pond, a population of zooplankton will also
develop, on which the fish feed. These natural live feeds help
develop the intense coloration desired in most koi. Unfortunately,
algae blooms prevent viewing the fish, so that sick fish can
go undetected for days or even weeks.
Algae influence the water quality of the pond
mainly by affecting the balance among dissolved oxygen, pH,
carbon dioxide, and nutrients. During photosynthesis, algae
produce oxygen, remove nutrients, and take up respired carbon
dioxide from both the fish and the algae itself. In heavily
stocked ponds, the water becomes supersaturated with carbon
dioxide. High levels of carbon dioxide can quickly depress
the pH of the water to levels below seven if the operator
is not careful to maintain proper alkalinity levels and adequate
aeration for stripping. During active periods of photosynthesis
(during daylight hours), algae can quickly strip the carbon
dioxide out of the water, and pH levels can rise above nine
in a matter of hours. Fish not acclimated to such sharp shifts
may initially show signs of stress.
At
night, both algae and fish consume oxygen from and exhale
carbon dioxide into the system. Algae compete with the fish
for available oxygen in the water. A potentially serious impact
of an algae bloom is the risk of an “algae crash”
triggered by temperature or barometric pressure. When an algae
bloom collapses, dead algae cells settle to the bottom of
the pond, adding to the decomposing sediment’s oxygen
demand. If the crash is severe, the pond’s oxygen supply
can be quickly depleted, endangering the fish unless backup
aeration is available. Additionally, as the dead algae cells
rupture, they can release organic nitrogen and phosphorous
back into the water, adding to the system’s nutrient
load. The biological cycle starts again with bacteria converting
the organic nutrients to inorganic elements. Which are then
available to be recycled, and the algae bloom continues.
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Practical Algae Control
View your pond as an ecosystem, one requiring you to manage
it to maintain proper balance. Fish ponds without adequate plantings
are most susceptible to algae bloom problems. These ponds are
usually well stocked with overfed fish. The absence of aquatic
plants eliminates competition with algae for available nutrients
in the pond water. Practical fish stocking densities and feeding
must be managed closely. |
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UV sterilization is a proven method for controlling waterborne
algae. Combining sterilization with adequate mechanical filtration,
and operating the two properly is most effective in eliminating
algae blooms and maintaining clear water. This combination
will not, however, control nitrogen or carbon dioxide levels.
Practical fish stocking densities and responsible feeding,
along with routine filter and UV sterilizer maintenance play
a big part in achieving a balanced system. Partial water changes
(approximately ten percent of the pond volume weekly with
non-chlorinated water) will aid in diluting nutrients. Filamentous
algae may grow and will benefit the pond by consuming nutrients
and carbon dioxide. Responsible fish feeding will encourage
the fish to graze on the filamentous algae, which is good
in their diet. Filamentous algae may also be harvested and
used as a fertilizer in gardens; remove it by hand or with
a long-bristle brush.
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