Good Pond Aeration is an essential requirement in all good Koi ponds. All Ponds need a plentiful supply of oxygen. Both your fish and the biological filter require large amounts of oxygen to thrive.

A good quality air pump such can power several air stones even at five or six feet depth. It is a good idea to place a few air stones directly in the filter system to provide oxygen for the filter bacteria as well as in the pond itself.

Oxygen will also be added by water splashing into the pond on its' return from the filter and waterfalls are especially effective in this respect. However, bear in mind if building a large waterfall the possible nuisance from the noise at night and also put in a system to bypass it in the winter. A large waterfall will have a big cooling effect on the water.

There is less need to worry about the oxygen level in the winter as cold water holds far more oxygen than warm water and your fish will be less active and require less oxygen.