Questions about overflow boxes

[NanoNoob]

I have a few questions about this overflow box that I hope someone can answer. Here is a pic of the overflow kit I purchased:

 

 

Here are the questions;

1. Why did it come with two U tubes? I thought you only need one. Is it an extra incase you two of them to keep up with the flow of the pump, or is it just a spare?

 

2. I understand the concept of it's operation (siphoning from the tank to the exterior box) but what will happen if the power goes out? Will the siphon break or be maintained? If it is maintained what stops it from sucking out all the watter in the internal box and finally, how is operation resumed when power comes back on and the pump starts pushing water again?

 

I know I am asking alot but any assistance anyone can provide is greatly appreciated.

 

Thanks

[Static]

If the power goes out, the water will keep draining from your tank untill it is at the same level as the divider in your external overflow box, then it will stop spilling over the divider and no more water will drain from your tank. Only the side of your overflow box with the drain hole will become empty. You are supposed to put the siphon tubes into the side of the overflow without the hole so that they will remain submerged in the event of a power failure.

 

As far as using one or both of the siphon tubes I would use both.

 

if your return line is submerged in the main tank you should make sure there is a hole near the water level in order to break the siphon it will become in the event of a power failure as well.

[Static]

http://www.melevsreef.com/sump.html

 

If you scroll down you will see an overflow that works on the same principal as yours. It's a slightly different layout, but it might help you picture how it maintains the siphon without draining the tank.