|Oxygen quite readily dissolves passively
diffusing from the atmosphere, but this limited
amount is insufficient to satisfy the demands
of koi and other oxygen-loving pond organisms
such as beneficial bacteria and invertebrates
in the filter.
Oxygen can often prove to be a limiting factor
for fish and biofilters with the health and
performance of both benefiting from additional
aeration, especially during the warmer summer
Aeration serves two purposes
The most obvious benefit of adding aeration
is to increase the dissolved oxygen concentration
to its maximum. This can be achieved in a number
of ways using water movement or the injection
of air. Besides ensuring an adequate exchange
of gases, aeration is also useful at helping
to mix and circulate water within the pond,
reducing the presence of dead-spots.
Air pump and diffuser ...
Air pumps are specifically designed for aerating
ponds. Working in a similar fashion to an aquarium
pump, a pond air pump is engineered to be able
to pump larger volumes of air to greater depths.
This is desirable, as to be effective, air must
be delivered to the very bottom of a pond to
provide the most efficient aeration and mixing.
The koi industry standard is the Hi-blow type
pump, which can deliver copious amounts of air
down to depths of 8 feet! Smaller pond air pumps
are available which amount to beefed-up aquarium
pumps. These are a cheaper alternative to the
Hi-Blow, but will not serve as many air stones
or no where near the depths of those reached
by the Hi-blows.
These diaphragm air pumps are silent running,
and will work tirelessly for many years between
diaphragm replacements. The replacement kits
for Hi-blows are considerably dearer than the
single diaphragms required for the smaller pond
A relatively new appearance on the air pump
market has seen the first fully-integrated battery
back-up air pump. This innovative unit constantly
senses the power supply, and should it be interrupted,
will automatically switch over to its auxiliary
battery back-up, which can enable it to pump
independently for 8 hours.
The air delivered by an air pump must be
used efficiently by an air diffuser, as this
will significantly affect its oxygenating performance.
The standard diffuser used by most koi keepers
is the golf-ball airstone. Extremely versatile,
inexpensive and durable, these can be placed
in the pond or into biological chambers to aid
the filtration process. More recent innovations
include porous pipe which can be installed on
the pond bottom or the ground breaking air dome.
An air dome consists of a circular perforated
rubber membrane mounted on a rigid backing plate
which is connected to an air supply. The membrane
forms a dome as pressure builds, releasing tiny
bubbles from each pore. This self-cleaning
diffuser really comes into its own when fitted
onto a bottom drain as its centralised mixing
action improves the performance of the bottom
drain. Ingeniously the air line can even be
traced down the bottom drain pipe to leave no
trailing air line in the pond to be snagged
Prices in UK:
Hi-blow pump - from 150
Smaller pond diaphragm pumps- 20-30
Air dome 50
Water movement can be used to aerate pond
water by injecting air into the water as it
A venturi is an adapted piece of pipework
which will draw air into a stream of water as
it is pumped into a pond from a filter chamber.
Venturis can look very impressive when viewed
from the pond side, but when observed underwater,
it is evident that the air bubbles are only
mixing and aerating the surface levels of the
pond water. They can also have the tendency
to obscure the viewing of koi and make quite
a noise to boot!
Waterfalls ... Waterfalls are natures way
of improving dissolved oxygen and they can be
used effectively to enhance D.O. in a koi pond.
They serve both an aesthetic and a functional
purpose but like a venturi will only aerate
and mix the upper layers.
In the winter, when D.O. is naturally at
its highest and the ponds oxygen requirements
are at their lowest, pond aeration, particularly
with a bottom diffuser should be ceased. This
will allow koi to settle in the deeper warmer
layers of water that will remain stable at the
air pond pump water aeration oxygen-loving
bottom diffuser koi Hi-blow diaphragm venturi
"air dome" mixing depths