Open Loop/Closed Loop

[Johnny Reefer]

Just need a little help understanding the definitions of "open loop" and "closed loop".

I've seen, a few times now, the words "closed loop" and "sump" used in the same sentence. [Internal overflow(s)].

Up to now I always thought that any sump system is an open loop and that something like a canister filter, say, is a closed loop.

I'm pretty sure that I understand that a sump system with external overflow siphon boxes is an open loop, but I am wondering....
Is a sump system with an internal overflow considered a closed loop?

Thanx much,

[mr_alberta]

Any loop where water can be added at any point to the system is an open system. So any system where water flows from one tank to another is an open system.

[Johnny Reefer]

'kay. Pretty much what I thought.

Thanx.

[BMW Rider]

A closed loop is basically a pump that pulls water from the tank and returns it directly to the tank. They are used primarily for additional cirrculation. A canister filter could be added to a closed loop, but generally with live rock systems additional filters are unnecassary. The primary goal of a closed loop is to increase water movement to promote stronger coral growth.