Why do you need to add an Air pump to a pond?
Koi & other fish require oxygen to breathe, oxygen is also required for bacteria in order to break down waste in the pond. There is more bactreia when there are higher oxygen levels helping to keep your water quality healthy for fish.
In Hotter weather in Summer, oxygen can be used by plants and algae at night, this will reduce oxygen levels. to prevent fish losses during warm weather it is crucial you have you air pump running 24 hours a day, every day.

What Air pump do you need?
We recommend that your air pump should be able to half of your ponds capacity each hour (for example a 2000 Litre per hour air pump, would be sufficient for a 4000 Litre pond). You cannot overdose on oxygen in your pond, however the more oxygen you have in the pond the beneficial it can be. For ponds with large stocks of Koi or other fish, more than one air pump on seperate electrical supplies is recommended, this can help ensure your fish would survive if one air pump stopped working.

Benefits of having an Air Pump
By having an air pump in your pond it will ensure your fish are safe in warmer weather conditions. If your pond pump ever stops working the air pump will act as a 'back up' and save your fishes lives until the pump is fixed/replaced.
The higher oxygen levels from the air pump will improve your water quality will higher volumes of bacteria.
An air pump can prevent your pond freezing over in colder months, as surface disturbance will stop it freezing.