Answer: 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 ? to 1 times per hour. A 500-galon 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.
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