The current or circulation in an aquarium is necessary for proper origination and aeration of the water. This is different than the flow of water through the filtration system. When discussing current it is specific to the actual water flow throughout the tank. In nature this is caused by rain, waves, tides, waterfalls, rapids, river flow, etc. An aquarium tank must mimic the natural water flow of the ecosystem it is showcasing. If the water becomes stagnant the oxygen levels drop suffocating the occupants. In order to create healthy currents powerheads are strategically placed in the tank. There are also wave makers available to simulate ocean tidal currents.
Laminar Flow – single direction flow from one end of the tank to the other
Turbulent Flow – water flow is completely random traveling in multiple directions
Surge Flow – water flows from side to side in a rocking motion
Flow rates differ depending on the type of tank needing circulation. The general rule of thumb is the more complex the tank the higher the flow rate will need to be. It is especially important to note that reef aquariums containing corals must have a turbulent flow. Corals are filter feeders meaning that water current brings food to them.