Choosing the proper pump for your pond or water garden can be a confusing and misleading process. Many retailers and dealers themselves are often unsure of how to make a proper pump recommendation. This often leads to incorrect information and the possibility of buying a pump not well suited for your unique water feature. Choosing the proper pump does not take much time, and is well worth the energy you put into selecting it. Among other things, the proper pump can save you money by consuming less energy, creating a healthier waterscape, 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 gallons
- Total dynamic head pressure
- Width of spillway on waterfall (if you will have a waterfall)
- Fish load
- Voltage/Energy Consumption
Total pond gallons can be figured out by using the following formula:
Rectangular or Square Pond: Length x Width x Average Depth x 7.5 = Approximate Gallons
Circular or Oval Pond: 3.14 x Radius x Radius x Average Depth x 7.5
It is important to know the approximate number of gallons 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 biofiltration.
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
11.3â€™ = 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 Gallons Per Hour and energy consumption at certain head heights. For example, you have 12 feet of dynamic head pressure. You calculate the proper pump for the pond would need to push 5200 GPH at this head pressure.
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. An example would be if there is a flat rock on top of the falls, the entire rocks width should be full of water spilling over when the pump is turned on. This is your spillway width. 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 gallons the pump will need to push in order to achieve the desired look. The formula for GPH needed per inch is as follows.
1 inch = 125 GPH
If the spillway is going to be around 22", a pump capable of at least 2750 GPH at that specific head pressure is needed. If a heavier flow is desired, increase the flow needed per inch to 150 or 175 GPH.
Fish Load is the total inches of fish per gallons 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 five gallons 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.
Voltage / Energy Consumption is the current of electricity your pump requires in order to operate correctly. Most pumps designed for ponds are wired for 110V, which can be plugged into any GFCI (Ground Fault Circuit Interrupter) outlet in the USA. If you intend on having a 230V pump, the principle explained later will apply. For energy consumption, a pump with the lowest wattage possible is the most appropriate. Each additional watt helps to build on the electric bill, which may be surprising when a pump is running 24/7. Generally, external pumps use less energy than submersible pumps when you get to the 3000 - 4000 GPH range and up. Also, most external pumps last much longer than submersibles. A good 6000 GPH external pump should be capable of running properly using no more than 450 watts, where as a standard submersible pump can use anywhere in the 750 - 1200 watt range. Just remember when making a selection to consider energy consumption. Remembering this can easily save hundreds of dollars per year on electricity.
There are many pumps available in the industry today. It is wise to consult with a pond professional before making a pump selection. Choosing the right pump can be complicated, but in the end, the time you spend selecting the most suited pump for your pond is well worth it for the safety of the fish, the beauty of the pond, and cost of the electric bill.