Submersible pond pumps can be placed directly in the pond and require relatively little installation. They are free of distracting noise, and for smaller ponds, can easily be utilized to drain your pond (if you hook up a hose to the output flow).
Pond Pumps are sized by gallons per hour (GPH) output at either zero or one foot of lift or height.
Submersible pumps are best suited to small to medium sized ponds with roughly 200 - 800 gallons of water. These are often the best choice because they connect easily to most of the submersible filters that are available for small to medium sized ponds.
Flow rates range from 250 GPH to as high as 4,100 GPH for a larger waterfall pump. Generally, the ideal pump will circulate the total volume of the pond at least once per hour. For example, if you pond is 500 gallons, you would want to go with at least a 500 GPH pump.