 Your pond set up relies on oxygen to
stay alive, but adding the right amount of this essential element requires a little
thought.
How does Aeration work?
Diverse populations of micro-organisms rely on a supply of oxygen
to keep them functioning effectively. Deny them oxygen and the water quality will
deteriorate; add extra and your pond will roar into life. Without oxygen filter
bacteria cannot oxidise and detoxify ammonia into nitrite and nitrate. If a pond or
filter is allowed to become oxygen-deficient for any period of time, anaerobic
conditions will prevail causing unstable conditions and the tell-tale bad egg
smell.
Dissolved oxygen in pond
water
The physical nature of water puts limitations on how much
oxygen we can expect it to hold. It also sets goals for what we should expect under
different conditions. The air we breathe is approximately 21 per cent oxygen, but in
any natural water body you will typically only find one percent dissolved oxygen
(DO), and usually less. So minute are the concentrations of DO in pond water that
levels are measured in milligrams per litre (mgI) or parts per million (ppm). 3mg of
oxygen dissolved in a litre of water equates to 3ppm. A number of physical factors
affect the levels of DO that can be achieved in any given pond.
Temperature
As water
temperature rises, its ability to dissolve oxygen reduces. Compare this to salt
which dissolves better in warm water, you can start to appreciate the unusual
relationship water has with oxygen.
Other Solutes
The presence of other solutions,
including salt and the liquid pond treatments, will also have a negative effect on
achievable DO levels. All the more reason to aerate vigorously under treatment
conditions.
Moving or flowing
water
Just as sugar dissolves better in a cup of coffee when it
is stirred, oxygen dissolves better in water that is more highly energised (flowing,
falling or cascading). In a natural environment energetic water courses, such as
highland streams, are higher in DO than lowland rivers. Oxygenated water that enters
a pond via a waterfall will rarely sink to the lower layers, being useful only at
the surface.
What you need to know
about aeration
The levels of DO achievable in a Koi pond are
determined by natural physical conditions that we have no control over, particularly
water temperature. We have various options when choosing an aeration device with
some methods proving more efficient than others. The most efficient method by far is
using diffused aeration, but the overall performance is still determined by the
careful selection of air pump and diffuser.
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