Allotment Articles 2.
Fish like all animals need oxygen to live even though they live in water. So it is necessary to maintain oxygen levels in the pool. In a densely stocked pond additional aeration will probably be needed. This can be achieved by the addition of a fountain or waterfall.
The action of agitating the water will cause more oxygen to be absorbed by the water. Some people use an air pump as used on fish tanks to blow air into the water that will also increase the amount of oxygen in the water. One method very popular with Koi keepers is the use of a VENTURI. This is a simple device that is attached to an outlet pipe from the pump where the water reenters the pond. Within the device is a restriction of the tubing with an air hole leading off it. This causes a change in pressure in the water flow that sucks in air, forcing it out in a stream of bubbles with the water.
The VENTURI works well with a fairly powerful pump and is available in various sizes. If no oxygenation devices are to be used in the pond stocking levels must be kept to a minimum. The maximum number of fish that a still pond will safely hold is 5 inches of fish per square foot. Only a fool would put in this many when stocking a fishpond, as this doesn't allow for growth. One or two inches would be a better stocking level.
Temperature also affects the absorption of oxygen into the water. The higher the temperature the lower the oxygen levels. This often explains why golden Orfe, which have a high oxygen requirement, die in a hot summer for no apparent reason. It is advisable during hot weather to apply some form of oxygenation to all ornamental ponds.
In the winter the temperature is low so the water holds more oxygen. This is very fortunate for nature, because it means that when the pond is frozen over for a short time, life can still go on underneath the ice. In prolonged cold spells it may be advisable to make an air hole to allow the gaseous exchange to occur. It is possible to buy test kits that check the oxygen levels, but they are expensive and a little common sense will remove the need to make tests.