What exactly is a closed loop system ?

A closed loop system is simply a stand alone pump that recirculates tank water. The benefits are added water flow to the display without added flow to the sump. A closed loop also lets you get rid of powerheads :thumbsup: by using multiple returns from the pump to the main display.
 
It makes sense that you can filter a closed loop system, but I've never seen it. Like eckrynock said, it's main purpose is to just recirculate the water. The perks of freeing up space (no power heads) and good water movement are beneficial for the life in your tank and is aesthetic pleasing.
 
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