Pumps come in a confusing array of models and sizes.You will need a pump if you are planning on moving water in your pond, whether by a waterfall, stream, fountain, or spouting ornament. This article will help you determine what size of pump you will need for your pond or water feature.It will not matter whether the pond has a liner, or if it is a preformed pond.
To operate any electrical equipment near a water garden, use an outdoor outlet. Set this outlet at least 6 feet from the water and use only an outlet that is equipped with a ground fault interrupter (GFIC) for safety. These devices will cut off the power the moment water is detected in contact with the wiring. Your cable should be protected in a conduit, a plastic tube for electrical wires, so you won’t dig into it accidentally. Extension cords with an integrated GFIC can be used for shorter distances. You can hide them under stones or mulch.
Pumps are available in both submersible and external (out-of-pond models). Reputable water garden suppliers have charts and other information available that can help you select the best model and connecting equipment for your purposes. For the smaller pond, a submersible pump is the most economical.
Pumps are sized by gallons per hour (GPH) output at one foot of lift or height. Larger capacity pumps are rated by horsepower (hp). Manufacturers offer charts that break down the power of each size pump according to incremental heights of one foot. Some companies label pumps by GPH while others assign letter or number designations that require cross-referencing to charts.
It is recommended that the water in a basic pond be turned between ½ to 1 times per hour. A 500-gallon pond should have at least a 500 Gallon Per Hour pump. When sizing a pump for a pond there are a few other considerations. How high will the pump have to lift water? Will there be a waterfall, fountain or statuary? Will there be filters? All of these variables reduce the amount of flow, which could affect water quality and clarity.
To determine the pump required for your pond, estimate the vertical height from the top of your pump to the top of your waterfall or stream. Add another foot of height or lift for every 10 feet of hosing you will be using. This will allow for loss of volume from resistance within the hose. A general rule of thumb is to figure your stream/waterfall requirement as 150 gallons per hour per inch width of the spillway or channel. For example, if your stream or waterfall spillway will be 10 inches wide, you will need a pump that produces a flow of 1500 gallons per hour (at whatever combined height of the feature and another foot of height for every ten feet of hosing to get there). You can use a valve to adjust the pumps flow to what you want. You cannot increase the pumps capacity. ALWAYS PURCHASE A PUMP THAT WILL MORE THAN HANDLE YOUR NEEDS.
Submersible pumps are placed directly in the pond.They are free of distracting noise and can be used to drain your pond when necessary. These pumps do have a disadvantage. The pump seal can rupture, sending oil coolant into the water. This can prevent surface gas exchanges, thereby endangering your fish. This happened to my pond only weeks after the pump was turned on. I would recommend the new magnetic-drive pump, which avoids the use of coolants. They are more expensive to buy but are far less expensive to operate.
I have been asked many times if you can use a swimming pool unit. This is very impractical for most people because they are very difficult to maintain. A pond has far more organic particulate matter (small separate particles) than a chemically maintained swimming pool. Sand is a fine medium that quickly clogs with debris. “Channeling,” in which water runs in limited paths, avoiding most of the filtration media, often occurs so that daily or frequent backwashing is required. Some pond keepers have adapted these units by using larder media, such as a proportion of gravel. Gravel is heavy and difficult to clean.
To select a pump, you will need to know how many gallons of water there are in your pond and what type of filtration, if any, you will be using. If you have a preformed pond, refer to the specification that comes with the pond. To calculate the water volume in a flexible-liner pond, see the chart below.
Calculating Water Volume
Rectangle Ponds. Length in feet x width in feet x depth in feet =cubic feet Circular pond. 3.14 (1/2 diameter in feet x 1/2 diameter in feet) x depth in feet = cubic feet. Free form shapes. Break the pond down into a series of rectangles and circles and figure the volume of each area separately, then add the volumes together. Each cubic foot contains 7.5 gallons of water, so multiply the total number of cubic feet times 7.5 to determine the total number of gallons.
Recommended Tubing Diameter For Pumps To Waterfalls.
1/2-inch diameter for flows up to 120gph
3/4-inch diameter for flows up to 350gph
1-inch diameter for flows up to 1000gph
1 1/4 inch for flows up to 1500 gph
1 1/2 inch for flows up to 3000 gph
Note: Thanks and credit goes to two wonderful friends, Helen Nash and Marilyn M. Cook, and their book ” Water Gardening Basics” Published by “Sterling Publishing Co.”
Safety Tip: To avoid accidentally pulling a pump cord out of its safety seal, secure the cord to the lifting handle on your pump with a plastic tie wrap. This will put the strain onto the pumps handle and not the cord.
Darlene Jennings (pond Lady) President,
Mid-Michigan Pond & Water Garden Club
Advanced MSU Master Gardener