Aeration is a very crucial element in a koi pond, every living thing in the pond requires a constant supply of oxygen. All serious Koi keepers have a dedicated aeration system running in their ponds and oft times in the biological chambers of their filters as well.
So why aerate a Koi pond?
In order to have a healthy, dynamic environment in your pond you will need a biological filter, a source of aeration, a circulation pump, and adequate space, or volume. It is important to note that all of these elements must work in harmony with one another.
The filtration system purifies the water of wastes, bacteria, and other toxins. An aerator supplies air to the water so the fish will have oxygen and the water does not stagnate. The pump moves the water through the filter and aerator. This cycle is the lifeblood of a pond.
Water ponds, fish, and oxygen ... the big secret to Koi fish keeping.
We survive on this earth because we can breathe oxygen. Koi need oxygen and the beneficial bacteria that keep the water healthy need oxygen.
Where is the best place in any pond system to add air or oxygen?
Directly into the biofilter system as close a possible to where the bacteria are sitting. This is why vortex filters and Japanese matting work so fantastically well together in any serious water ponds system .... but only by pumping plentiful volumes of air around the Japanese matting matrix.
How much air should you add to you, Koi Pond?
Add as much air to your pond as you can using air pumps and air stones to distribute the air (highly recommended for ponds that are heavily stocked). You can add the air directly to the pond, the filter, the waterfall and anywhere else you can think of.
These numbers are intended as a guideline. Your application may vary according to stocking levels. (In general terms, 40lpm per 1000 gallons is a good rule of thumb.)
The amount of oxygen water can hold is dependent upon atmospheric pressure, salinity, and temperature. Water can hold less oxygen as altitude increases. Salinity is not important for most freshwater fish producers. The most important factor is water temperature. As temperature increases, water can hold less oxygen. Most low oxygen problems occur from June through September. The reasons for this are:
The last note for safety
NEVER - NEVER install an air pump BELOW water level! (Unless you install a check valve in the line!) If at any time your power supply to your air pump is interrupted, water will back siphon down the delivery tube and flood the pump workings, rendering the pump inoperative, to say nothing of the danger of water and electricity coming in contact.