new tank drilled in the center? why
 

So the nabour gave me a nice 5 ft 125 it had the bottom drilled right in the center just wondering why is in the center instead of the side. Rght now it's got a peace of glass over it and does hold water but i would like to make it a drilled tank again but why whould it be drilled in the center please and thanks

Possible it was used for a closed loop set up. Does it have an overflow or any other holes ?

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)

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

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

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.

http://i49.photobucket.com/albums/f2...h/IMG_1281.jpg

nice center OF tank fr the OM forum, here's the post