Submersible water pumps represent the largest group of aquarium and pond water pumps. There are a few different classes of these pumps depending on their primary use. All, however, use a magnetic energizer motor and rotating impeller design to create the water flow. This design makes them water proof and allows them to be submersed.
Perhaps the simplest class is the powerhead pump, designed to be used with an UnderGravel filter system and sit on top of the “lift tubes”. A great example of a powerhead pump includes the Maxi-Jet. These were the first submersible pumps in the aquarium hobby.
A second class is designed to provide large scale water movement by the use of a “prop” style impeller. These pumps, including the Koralia, Fluval Sea, Aqueon, and SEIO, generally mount to the back or sides of the aquarium to provide currents, especially in the mini-reef aquarium. Most are designed to work with wave making timers to provide counter currents in the aquarium.
The last group of submersible pumps is what most people think of when they think of a water pump. These pumps have moderate to high flow rates and may or may not have true plumbing connectors. They are rated to push water a certain “head height” and mostly serve as a means to transport water from a sump filter back up to the aquarium, or from the bottom of the pond to the top of a waterfall.
Nearly all submersible pumps produce very little noise, perhaps a constant hum that blends into the background. The impeller is the only moving part and will require maintenance and can be replaced when needed.