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What Size Pump Do You Need For Your Pond?

Pond with flowers and fish

A pond pump, an essential supplement to any pond that is in motion, benefits both the plants and the wildlife in the pond. Pond pumps also ensure an adequate water flow and help to maintain a healthy pond ecosystem.

The first step in determining what size pump a pond needs is to calculate the water flow requirements. There are several steps involved to determine this figure. It is important not to underestimate the amount of water needed in a waterfall; this is a mistake often made by new pond builders. They assume that one thousand GPH (gallons per hour) provides a good supply, but this amounts to just a fifth of a gallon per second. This small amount spread out over a 2-foot waterfall will barely create more than a small trickle.

Fifty GPH spread over a 24-inch fall will yield a trickle that is about ΒΌ-inch deep. Two hundred GPH will give a strong dramatic water flow about one inch deep that can be heard from more than thirty feet away.

For maintaining water not harboring fish, expert pond builders agree that all water in the pond should be circulated at least once every two hours. If a pond contains 2,000 gallons of water, you will want a minimum of 1,000 GPH flow.

To maintain water that does harbor fish, more filtration is required. It is recommended that the water flow be doubled to improve the purity of the water. In a 2,000 gallon pond, there should be 2,000 GPH water flow.

Once the amount of flow needed has been determined, the required pump size can be calculated. The performance of a pond pump will vary depending on how much resistance is required to drive the water upward. Total dynamic head (TDH) is the term used by professionals to gauge the pressure on a pump caused by the interactions of flow rate, pipe length, pipe diameter, pipe material and any elevation. The greater the resistance a pump encounters, the slower the flow will be. For maximum efficiency, a pump that can compensate for TDH should be purchased.

The formula to determine the TDH in any given pond is as follows.

  • For every foot of vertical lift, or for every foot from the surface of the water to the top of the pond, add one foot head pressure
  • For every 90-degree lifting, add two feet head pressure
  • For any other type of lifting, add one foot head pressure
  • For every 10 feet of pipe or hose, add one foot head pressure

Combine the amounts from the calculations above to obtain the total footage head pressure. As an example, in a pond with thirty feet of piping, a 4-foot waterfall and two 90-degree fittings, the addition is as follows:

  • Distance from vertical lift of waterfall — four feet
  • Footage of pipe — three feet
  • Two 90-degree fittings — four feet

Total = 11 feet of head pressure.

The pump size required for a pond can be determined using the pump performance chart, the calculated head pressure and the amount of flow needed.