Ponds that are ecologically balanced with plants and a few fish do not absolutely require a pump for recirculation and aeration. However, water movement adds to the aesthetic enjoyment of the pond and contributes to the well being of fish. The addition of water features such as waterfalls, fountains and statuary as well as various types of filtration require appropriately sized pumps. When in doubt, choose a larger pump. It is easy to decrease the flow, but impossible to increase the flow beyond the pump capacity.

Factors to take into account
Mechanical Filtration:

The general recommended flow rate is 1/2 the pond volume per hour.

Biological Filtration:

Biological filters have a specific flow rate according to manufacturer and size. Slow flow rates allow the aerobic bacteria more exposure to the water to break down impurities. A fast flow may actually dislodge the bacteria from the filter.

Waterfalls: Factors to consider:
1) the height of the waterfall above the pump; the higher the waterfall, the larger the pump needed.
2) the horizontal distance from the pump to the top of waterfall, or discharge point. 10′ horizontal distance = 1′ of height or “head”.
3) the width of the waterfall and the effect desired.

“Standard” waterfall: with a 1/8″ to 1/4″ film of water 12″ wide requires 200-300 gph of flow at the top of the waterfall.
“Rushing” waterfall: with a 1/2″ to 3/4″ film of water 12″ wide requires 700-1200 gph of flow at the top of the waterfall.
Calculating Pond Capacity
Calculation of Pond VOLUME is important when choosing a filter. SURFACE AREA is important for stocking fish and plants.

Shape of Pond
Pond Volume (US Gal)
Surface Area (sq. ft.)
Rectangular or Square
Length x Width x Depth x 7.5
Length x Width
Radius x Radius x Depth x 23.55
Radius x Radius x 3.14
Oval with straight sides
Length x Width x Depth x 6.7
Length x Width (approx.)