All aquariums require water movement in some form – even those
simulating a quiet, sheltered pool. Water movement aids
aeration/oxygenation of the water, filtration, transfer from a sump
to the main tank, creation of currents and even the simulation of
tidal movements.In general, this is achieved by the use of
different kinds of pump.
obviously, these are used for pumping air into an aquarium (usually using an airstone), but are also used to power simple protein skimmers. The effect of bubbling air through an uplift tube drags water upwards with it – this means air can be used to power under-gravel filters. This however, doesn't create a very powerful flow so a powerhead is potentially more effective.
these have numerous uses – transfer of water from a sump to the main aquarium, to power under-gravel filters and to create flow within the aquarium itself. This is obviously important in creating a fast flowing environment for certain fish and particularly so in marine/reef aquaria – there are some extremely powerful pumps made especially for this purpose. Even so, it is difficult to create flow sufficient to even nearly match that observed in nature. These can be attached to a wavemaker device which switches pumps on and off in turn in order to create a random flow – important in a reef tank.
these specialized pumps are used for more accurate, usually slower, flow control, perhaps for feeding water through a de-nitrator. They are also used for precise dosing of chemicals or medications. They work differently from other pumps in that a roller with 2,3 or 4 raised edges rotates and, in doing so squeezes liquids through a tube.