Maintaining Oxygen Levels in Fish / KOI
Severe environmental stressors
are the most frequent causes of sudden
fish death in garden ponds or other fish habitats, and the lack
oxygen in the water is the number one stressor of all.
Two major factors contributing to fish-pond oxygen loss concern
algae. During daylight hours, algae make oxygen; during the
however, the plants take oxygen. If algae are profusely
plants deplete all the pond’s oxygen during the night, which in
causes fish inhabiting the pond to die.
Another way that algae trigger oxygen loss is by dying suddenly.
Algae-bloom death occurs naturally or from chemical treatment of
algaecide. When algae die suddenly – from either cause – the
oxygen becomes quickly depleted because the algae no longer are
alive and making it.
Then, when dead algae begin to decompose, the decaying process
further depletes oxygen. Fish have been observed gulping for
the water’s surface in sixty minutes or less from the onset of
In ponds stocked liberally with many fish, often the oxygen
just adequate enough to sustain them. If any further claim on
existing oxygen is made, this delicate environmental balance
upset. When no or inadequate aeration is provided, along with
warm-weather water temperatures, the conditions for fish
survival become critical.
As water warms, its oxygen-retaining capacity decreases.
small fountains, waterfalls, or other water-aerating devices are
incapable of providing adequate oxygen for fish. Additional
should be introduced through brisk aeration when fighting algae,
importantly when water temperatures surpass eighty degrees
Testing devices are the only sure method to accurately read
levels. Because these devices are not usually on hand for the
person maintaining a water garden or fish pond, the easiest way
ensure sufficient oxygen levels is to provide generous and
aeration. Pumps and diffusers that “bubble” air into the water
waterfalls, fountains, and other “splashing” water devices are
ways to get sufficient oxygen into the pond. When the weather is
or if an algae problem exists, it is imperative that
aeration be provided constantly, throughout the day and night.
One other algae-caused loss of fish has gained attention and is
studied in areas around the world. These fish-killing algal
contain potent toxins that trigger sudden fish death. If a pond
these particularly virulent algae, devastating fish loss can
seemingly more so when a quick die-off of algal bloom occurs.
discharge their toxins concurrently, and some or all fish in the
are adversely affected or killed. Fortunately, since pond owners
unable to identify these algae, this danger is rare.
Keep your oxygen levels under control at all times and you will
increase your the lifespan of your fish.
One excellent way to enhance oxygen levels in
your pond, is to add an
air pump or aerator.
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