Koi College - Perfect Koi Pond
It is generally accepted that 4 inch bottom drains are a must and should be fitted to all ponds. Bottom drains are designed to be placed at the deepest part of the pond for the removal of the wastes and the settlements. Some 4" bottom drains come with aeration. Aerated bottom drains must have an air pump to work. As the drain cover gives some oxygen back to the water column it also gives off tremendous circulation and a sweeping action. Bottom drains count for the majority of the water circulation in a Koi pond. The vast majority of solids will sink to the bottom of the pond in time, where ideally, they will be sucked into the bottom drain and end up in the filter systems where they will be extracted from the water column by the vortex settling chamber then converted to nitrate by the nitrification process in the Bio-Chamber.
Note: A single drain will sweep a 6 to 7 foot radius, larger ponds need more drains. Do not install a bottom drain with less then a 4 inch outlet, smaller drains block easily and restrict flow, remember these drains are gravity fed. 1 drain 1 pipe no tees.