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Choosing your Pond Pump

Do I need a pump for my pond?
Yes. Most ponds require water movement to maintain a healthy, well-balanced pond or to create an impressive water feature. Moving water can offer benefits to any type of water feature in the form of recirculation, aeration, and ornamentation. The best way to move water in a pond is by installing a pump. Pumps can recirculate the water within your pond or water garden, distributing the water's beneficial nutrients to all aquatic life in the pond. Additionally, running water prevents stagnation and insures that oxygen levels remain evenly distributed throughout the pond. This circulation guards against pond turnover, which occurs when the uppermost layers of water suddenly drop in temperature and mix with the deeper levels of oxygen-depleted water. Such a turnover causes an overall loss of oxygen for fish and other aquatic life and often leads to pond kills. Additionally, moving water inhibits algae and prevents mosquitoes from laying eggs on the water's surface.

Even if your pond is solely ornamental, a pump will be required to prevent stagnation, inhibit algae growth, inhibit insect pests, and to power a decorative water display. Stagnant water tends to have a distinctive, unpleasant scent, which is generally undesirable for an ornamental pond. Streams, waterfalls, fountains, and spitters all require a pump.


What type of pump do I need for my pond?
Several types of pond pump exist, and you can be sure that there is a pump that will suit your particular needs. Pond pumps are typically categorized by the way they work, as magnetic drive pumps or as direct drive pumps. Each pump may also be classified as submersible or as external, sometimes referred to as in-line. Whatever pump you decide is right for your pond, keep in mind that it is imperative that you buy a pump suitable for pond use. Pumps not designed for ponds typically are not as efficient and will burn out quickly. Trash pumps, aquarium pumps, and sump pumps are most commonly used in the place of pond pumps, and none of them tend to stand up to the rigors of pond use as they are not designed to run continuously. We will outline the different types of pond pump, discussing the positive and negative aspects of each.

Magnetic Drive
Far and above, magnetic drive, or mag-drive, pumps tend to be the best pump for the job when it comes to ponds. In a magnetic drive pump, the electricity from your outlet creates an electromagnet that drives an impeller and magnetic shaft. When a mag-drive pump is plugged in, the magnetic shaft and impeller will spin in the magnetic field created by the electromagnet to push water through the outlet of the pump. This method of pushing water tends to be far more energy efficient than in other comparable pumps. Mag-drive pumps tend to be a little pricier than other pumps, but usually pay for themselves in less than one season due to their tremendous efficiency.

Magnetic drive pumps are perfectly safe for ponds stocked with fish as there is no danger of oil leaks. Mag-drive pumps are completely sealed and do not need oil for lubrication due to their innovative electromagnet-driven mechanism. Because of this design, however, mag-drive pumps are limited in their ability to push water to significant head heights. Also, these pumps are only able to push water, they are not self-priming and are unable to draw water to them. In the event that a mag-drive pump were to stop working, replacement parts are commonly available and are easily installed by even the least mechanically-inclined. Most often, the only repair needed on a mag-drive pump is replacing the magnetic shaft and impeller as it is the only moving part.


Direct Drive
If you are looking to power a water feature with a considerable head height, then a direct drive pump is most likely the pump for you. Direct drive pumps use electricity to power a motor which physically turns a shaft and impeller. This mechanism leads to a higher energy bill, but the pumps themselves tend to be less pricey.

Traditionally, direct drive pumps have required oil as lubrication as the shaft and impeller are physically turned by a motor. These models tend not to be appropriate for ponds stocked with fish as there is a danger of oil contaminating the water. Newer trends in direct drive pumps, however, are to use other forms of lubrication or epoxy rather than oil. These models are perfectly fish safe.

Although they use a substantial amount of energy, direct drive pumps will pump water to more extreme heights than their mag-drive counterparts. Also, unlike mag-drives, direct drive pumps are often self-priming and will draw water to them.


Submersible
Submersible pumps refer to models of pond pump designed specifically to be installed entirely beneath the surface of the water and are usually placed in the deepest part of the pond. Be sure to check the cord length when choosing a submersible pump to ensure that it will reach your electric outlet with a ground fault circuit interrupter (GFCI). Installing a submersible pump is typically very simple. Just place the pump and filter (if applicable) in the water. Maintenance on a submersible pump is less convenient than on an external pump as the submersible pump must be pulled from the water routinely to clean its pre-filter or screen.

The unobtrusiveness of submersible pumps allows them to be used in pond designs that incorporate more natural settings, as you do not have to hide or camouflage the pump. Submersible pumps also run quietly and will not disturb any outdoor activities.


External
External pumps refer to models of pond pump designed to sit completely out of the water. Because they sit outside the pond, external pumps, or in-line pumps, tend to require more time and effort to install but are more convenient and require less routine maintenance than submersible pumps.

Keep in mind that when purchasing an external pump, you may need to hide or camouflage the pump if you prefer a more natural looking pond or are concerned about equipment being visible. Also be sure to check whether or not your pump is self-priming, or able to draw water to itself. If you install an external pump that is not self-priming, you may need to take extra measures to ensure that your pump does not burn up in the event the power should go out and return. Installing a check valve or placing the pump below the water level (digging a hole), can prevent the pump from running dry and eliminate some of the need for a self-priming pump. External pumps are often loud and could disturb your outdoor activities.


What size pump do I need for my pond?
This question's answer is largely dependent on your needs. As a pond owner, you must decide whether your pump will be used for filtration, used to power water displays in an ornamental pond, or for recirculation. We will outline some of the variables that will affect your choice of pump for each of these functions.


Filtration
In order to filter your pond with maximum effectiveness, its entire volume should be circulated at a rate of once every hour; and at a minimum, its volume must be circulated at a rate of once every two hours. Your pump must be chosen with these concepts in mind. For instance, if your pond were 2,500 gallons, the pump you choose would need a 2,500 gallon per hour (GPH) rating to achieve maximum effectiveness and 1,250 GPH at a minimum. However, it is always better to err on the side of caution by choosing a pump one size larger than the one you calculate for your needs. Remember that a pump's output may never be increased, but it may be reduced or restricted very easily through the use of a common ball valve. A 3,000 GPH pump may be restricted to only circulate 2,500 GPH, but a 2,000 GPH pump can never circulate more than its rating. Be sure to check the pump compatibility of your filter before making the final decision on a pump. Your filter should list a maximum pump flow set by its manufacturer. Choosing a pump with a flow greater than the filter recommends can jeopardize the effectiveness of the filter and lead to an unhealthy pond. If waterfalls, fountains, or other decorative water features are present, you should consider running a separate pump for that feature or features. This will ensure that your water feature will run consistently despite the status of your filter.


Water Features
Whether your water feature is a trickling stream or thundering waterfall, a pump will be responsible for making it flow. Choosing the appropriate pump for this application is, again, highly subjective and depends upon your personal preference. However, there are some helpful methods of determining what pump will best suit your needs. For instance, for most streams, waterfalls, and features you can approximate the size pump you need by using a garden hose. A standard 5/8" garden hose has a flow rate between 850 GPH and 900 GPH. By running a standard garden hose at the source of your stream, waterfall, or water feature, you can get an idea of the size pump you will want. If the flow produced by the garden hose is not as dramatic as you would like your feature to ultimately have, then use it to approximate the flow you would like. For example, if you would like the flow to be about twice as much, then you are looking for a pump with a flow rate of between 1,700 GPH and 1,800 GPH at the given head height.

Head height refers to an approximation of the distance (both horizontally and vertically) through which a pump will need to push water. Every ten feet of pipe through which water will travel horizontally contributes 1 foot of head height (10:1 ratio) while every vertical foot also contributes 1 foot of head height (1:1 ratio). If you were to install your pump 30 feet from your water feature, which was 4 feet above the ponds surface level, your water feature's head height would be 7 feet (horizontal distance contributes 3 ft and the vertical height also contributes 4 ft).

(Horizontal distance / 10 ft) + (vertical height above water level) = head height

So if you calculated that your stream, waterfall, or feature needs a flow of 1,800 GPH through the garden hose approximation technique and your water feature's head height is 7 feet, then you need to find a pump whose GPH meets or exceeds 1,800 GPH at 7 feet of head.

For a more precise method of measuring the flow a stream or waterfall will require for a given effect, you may wish to use the following calculations:


Trickle (1/8" deep) =100 GPH per 4" of ledge

Medium (1/4" deep) =100 GPH per 2" of ledge

Dramatic (1/2" deep) =100 GPH per 1" of ledge


For instance, if your stream or waterfall is 24" wide and you would like a trickle, then you will need a pump with a flow that is equal or greater than 600 GPH at the feature's given head height. You will need a pump with a flow equal or greater than 1,200 GPH for a medium flow and 2,400 GPH for a dramatic flow at the feature's given head height.

When considering a pump for fountains, statuary, and spitters, be sure that you follow the manufacturers suggested pump flow. Be sure to check the pump compatibility of your features before making the final decision on a pump. Your features should list a recommended pump flow set by its manufacturer. Choosing a pump with a flow outside the feature's recommended rates will influence the overall look of the feature. If a filtration system is also present, you should consider running a separate pump for the filter. This will ensure that your water feature will run consistently despite the status of your filter.


Recirculation
Circulating the water in your pond will ensure that your pond's beneficial nutrients are distributed to all aquatic life and prevent pond turnovers or destratification. Using a pump in one or both of the aforementioned applications will result in some recirculation in your pond. Choosing the proper filtration system and pump for your pond will adequately recirculate your pond's water. Ornamental water displays will help recirculate your pond's water, but may not always adequately distribute nutrients or prevent turnovers, stagnation, and thermal stratification.