An important and often overlooked part of the aquarium is water motion. Water movement is important for oxygen exchange, waste removal, calcification and many other physical processes.  There are many types of products to facilitate this, from small powerheads to water switching devices and wavemakers.  Powerheads provide an easy way of circulating water within the tank, but can often detract from the beauty of the tank.  Water switching devices offer an external option  whereby water is plumbed outside the tank and enter the tank by a less visible manner.