Pond Pump Selection Guide
Proper pond pump can save you money, creating a healthier waterfeature, and are often times less expensive and less maintenance than most people imagine. Factors to consider when choosing a pond pump are as follows.
Total pond Litres can be figured out by using the following formula:
Rectangular or Square Pond:
Length (mt)x Width (mt)x Average Depth (mt) x 1000 = Approx volume of pond in litres
Circular or Oval Pond:
3.14 x Radius (mt) x Radius (mt) x Average Depth (mt) x 1000 = Approx volume of pond in litres
It is important to know the approximate number of litres in your water feature to be sure that insufficient circulation does not occur. Insufficient circulation can cause areas of stagnant water, unacceptably low oxygen levels, lack of proper filtration, and many other things, which will eventually lead to an unhealthy pond. Unhealthy ponds are not good habitats for fish and plants, and will become an unpleasant addition to the backyard. By choosing the proper pump, many of these harmful conditions can be prevented. Rule of thumb is to circulate the pond water a minimum of once every two hours. Generally, the more circulation the better, with exception to bio filtration.
Total dynamic head pressure is the amount of total pressure put back onto the pump while the pump is in operation. The greater the head pressure, the less your pump will circulate water. Dynamic head pressure encompasses many things including the amount of tubing the water needs to be pushed through, the height from the top of the water level to the top of the push for the pump (eg: waterfall), the tubing diameter, any special bends or adapters including ball valves and gate valves and other special fittings. To make it simple and to find an approximate head pressure, calculate the following for your situation:
A = The vertical height (in feet) from the top of the water level to the top of the water push. (e.g. waterfall)
B = Total distance of tubing (in feet) the water needs to be pushed through.
C = Number of 90 degree bends and reducers.
D = Number of miscellaneous adapters such as ball valves and bulkheads.
A + (B / 10) + (C / 2) + (D / 4) = Approximate Head Pressure
A = Vertical Height = 4.5’
B = Total Distance = 28’
C = Number of 90 degree bends and reducers = 2
D = Number of misc. adaptors = 12
4.5 + (28 / 10) + (2 / 2) + (12 / 4) = Total Dynamic Head Pressure
4.5 + 2.8 + 1 + 3 = Total Dynamic Head Pressure
11.3’ = Total Dynamic Head Pressure
Now that an approximate total dynamic head pressure is determined, you are better able to make a pump selection. The higher the number, the more pressure the pump is going to be under, which means it will pump less. Most pumps have a "flow chart,” indicating such specifications as Litres per Hour at certain head heights.
Width of spillway on waterfall is the width of the sheet of water, which will be needed by the waterfall. If there is a stream, that can also be used as your spillway measurement. The width of the spillway should be figured in inches for the following equation. Once you know approximately how many inches wide the spillway will be, you can now obtain how many Litres the pump will need to push in order to achieve the desired look. The formula for LPH needed per inch is as follows.
1 inch = 470 LPH
If the spillway is going to be around 22”, a pump capable of at least 10340 LPH at that specific head pressure is needed. If a heavier flow is desired, increase the flow needed per inch to 600 or 700 LPH.
Fish Load is the total inches of fish per litres of water. There is no true definition on how to figure this value out, however, the more fish you have, the more filtration and circulation the pond will require. Generally speaking, it is acceptable to have five inches of fish per 20 litres of pond water. It is valuable to keep the fish load below the accepted equation. If the pond is solely for fish, more flow and circulation is required than a pond that is filled with plants and fewer fish. Excluding bio filtration, the more flow the better, especially if there is a high fish load. Keep this in mind when choosing the right pump for your application.