Air Supply

Why Aerate ?

Oxygen is vital to the wellbeing of virtually every living thing on the planet. Especially your Koi and filter bacteria.

Either mg/litre or ppm are used as units of measurement for Oxygen content. It makes no difference which you use because they are equal measures with 1mg/litre = 1ppm. When a body of water can hold no more oxygen it is termed saturated and the amount of oxygen the water contains at this saturation point varies with height above sea level, salinity i.e. how much salt is in the water and, most of all, temperature.

In an ideal world the water would be 100% saturated with oxygen at all times but this is very difficult, if not impossible, to achieve. Fortunately, the animals in your pond eco system do not require 100% saturation and a level of 80% will usually be acceptable. This level gives a safety margin in case of extra demand due to overfeeding, low atmospheric pressure etc.

The number of fish in your pond and the water temperature will have the biggest effect on oxygen demand as more fish in warmer water will eat more and produce more waste with more bacteria required to break it down.

Aeration is the process by which air and water are brought into intimate contact and the exchange of gases becomes possible at the air/water interface of every bubble. An air pump connected to diffusers or airstones to introduce bubbles to the water will aerate the water and help maintain high levels of oxygen in our ponds.

Because this aeration happens while the bubble is rising, and only at it's surface, the smaller the bubble and the slower it rises the more oxygen will be able to pass into the water. A comparatively gentle stream of very fine bubbles will achieve best oxygenation of the pond water.

A large output airpump connected to a single diffuser or airstone looks impressive as it makes the water "boil" but it is far better to spread the output over several diffusers for maximum beneficial effect.

The time to introduce extra oxygen into the pond is usually during warmer weather. When the water is warm it can not hold the same amount of oxygen as when cold but, as we know, Koi feed voraciously in warm water and in so doing they unfortunately produce lots of waste. This can be minimised by feeding a high quality food but you will still need to provide high levels of oxygen to maitain both Koi and filter in peak condition.

The time NOT to introduce air into the pond is overwinter when you may be pumping in air which is colder than the water and so cooling it uneccesarily and countering any heat you may be putting in.

For interest, here is a chart showing the effect of temperature, height (atmospheric pressure) and salinity on the amount of oxygen in water at saturation point.

Oxygen Saturation Point
Temperature		Fresh Water mg/litre		Salt Water
°F	°C	Sea Level	2,000 ft.	@ 35,000mg/litre (Sea Water)
50	10	11.3	10.5.	9.0
59	15	10.1	9.4.	8.1
68	20	9.1	8.4.	7.4
72	22	8.7	8.1.	7.1
75	24	8.4	7.8.	6.9
79	26	8.1	7.5.	6.6
83	28	7.8	7.3.	6.4
86	30	7.5	7.0.	6.2