what is closed loop?
 

I have no idea what a closed loop is or what it is used for, any help?

A closed loop is when water drains from your tank to a pump return. The closed part is that there is no opening in the system except within the tank, all the external plumbing is sealed (closed). It's a way to provide flow without an overflow or sump.

so having a sump makes this of no use to me...?

[url]http://www.melevsreef.com/closedloop.html[/url]

This is an example of a CL. It will give you more flow and can reduce the number of power heads in your tank. They are used just for water movement really

ebmorri