This section will assume that only aquatic plants are going to be present. It is recommended that the water in a basic pond be turned once per hour. A 500-gallon pond should have at least a 500-Gallon Per Hour (GPH) pump. When sizing a pump for a pond there are a few other considerations. ~ How high will the pump have to pump water? ~ Will there be a waterfall, a fountain, and/or small statuary? ~ Will there be filters? All these variables reduce the amount of flow, which, in turn, could affect water quality and clarity. In most situations, adding 25% more pump capacity is adequate. Therefore, using the example of a 500-gallon pond with a 3' waterfall, the pump's flow rate should be a minimum of 625 gallons per hour. Keep in mind that restricting the discharge with a valve or a clamp on the vinyl discharge tubing can reduce the flow of a centrifugal pump. A 700 GPH can be reduced to 625 GPH, but a 500 GPH pump will only pump a maximum of 500 GPH. When a biological filter is used, care should be taken not to oversize the pump. Biological filters require a certain amount of flow. Check with the manufacturer of the filter for correct pump size. The basic formula to compute the gallons of a pond is: Length x Width x Depth x 7.5. Example: 10' x 20' x 1.5 x 7.5 = 2250 gallons. The pond should have a pump capable of pumping 2250 gallons per hour (not using a garden hose, but using the full discharge).