A closed loop is when you have a pump that pulls from the display and returns to the display creating a “closed loop” of flow within the display. They are typically external pumps and their primary purpose is to provide flow in the display. Most don’t use closed loops anymore and instead use power heads/wave makers since they are very efficient and create good controllable flow within the display. A closed loop differs from a return pump that pulls from the sump and returns to the display.
Closed loops still have a place in our hobby in my opinion and can be very useful. They allow you to provide flow in places that power heads don’t reach. Places such as behind the rocks or in my case, below the rocks where my closed loop pump returns to. In my case, it prevents detritus from settling under the rocks or on the bottom of the tank because my closed loop exhausts through a manifold that circles my overflow below my rock. I pump several thousand gallons an hour through my closed loop depending on the time of day and it’s also synched up with my Tunze’s via 0-10v control. When my Tunze’s go into flush mode to suspend detritus, my closed loop kicks up to about 6000 GPH and blasts any waste that might have settled on the bottom and suspends it so the Tunze’s can push it up high into the water column so that my returns can push the detritus into my overflow.
With a closed loop you can have it take water in from one side of the tank and return to another which is also nice since a power head pulls from the same place it pushes from. If you run a UV sterilzer like I do, a closed loop pump is the best/most effective place place to run one from since it’s constantly circulating water from the display back to the display without going through the sump. This makes for the most effervescent use of UV sterilization in terms of water born algae control, parasite reduction, nuisance bacteria control etc.
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