To choose the right size pond pump, first determine the proper application category: 1) Filtration and Recirculation; or 2) Water Features.Filtration and Recirculation: The general rule of thumb for filtration and recirculation applications is the pump should turn the pond water over a minimum of once every two hours, and ideally once an hour. For example, if your pond is 3,000 gallons the ideal pump size is 3,000 GPH, but not less than 1,500 GPH. My personal preference is to always err on the high end of the range. A pump's flow can always be slightly restricted, but never increased. Also, make sure your pump is the right size for your pond filter's specifications.

Water Features: Choosing the correct pump size for a water feature is a bit more involved. The first step is to determine how much water flow you need at the discharge point of the water feature itself. Let's use a waterfall as an example as this is the most common water feature. For each inch of waterfall width you need 100 to 150 GPH. So, if you have a 14" wide waterfall weir you will need 1,400 GPH to 2,100 GPH of water flow over the lip of the weir.

The next step is to calculate the head height. Head height refers to the approximation of the vertical and horizontal distance the water must travel from the pump to the top of the waterfall. Horizontal distance is calculated at a 10:1 ratio, while vertical distance is calculated at a 1:1 ratio. For example, if the horizontal distance from the pond pump to the waterfall is 30', this equates to 3' of head height. If the vertical distance from the pump to the top of the waterfall is 7', this equates to 7' of head height. Therefore, the total head height for this application is 10'.The last step is to review the manufacturer's power curve for the type of pump you have selected to determine the appropriate pump size. Let's use the Cal Pump Mag Drive as an example. The PWM3900 model is rated at 4,100 GPH of water flow at the pump discharge, but is rated at 2,280 GPH of water flow at a 10' head height. This would be a good choice for this particular example. Remember, it is always better to err on the high end of the GPH range as this will put less strain on the pump.

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