new tank drilled in the center? why

[parkinsn]

I would say it was the start of a closed loop or it was going to viewable all 4 side's with a center overflow possibly (but not likely)

[damtrees420]

how does the closed loop work or should i just leave sealed up and buld my own over flow somehow id like to plum it in to my other tank and have both running off one sump

[parkinsn]

Its basicly a powerhead(s) without the powerhead. Essentially its an intake (your center hole) with an external pump that circulates your water, generally via drilled holes in your tank, but I guess you could go up and over the top. So the water never really leaves your tank. Adding circulation without hitting your sump (which would be an open loop) have a look at Snappys tank, his intake is in his overflow box and the holes drilled in the back are the returns. Page's 8-13 will show you this. Kinda hard to explain with out looking at it.

http://reefcentral.com/forums/showth...459184&page=12

[The Grizz]

Closed loop start about here :

http://www.canreef.com/vbulletin/sho...=60533&page=16

on my tank build, you have to go through a couple page's before you see the whole thing.