holes in a drilled tank

[ibranny]

there are three holes in my tank two is being used send/return for sump what would the third hole be for?

 

[maelv]

??? Drain for a closed loop system that would be brought back up over the top maybe?
Could be one drain into the sump, and two returns back to the tank???
Hard for me to say, but those are a couple of ideas.

 

[ibranny]

so with two returns and one drain. will i still need powerheads or will this drive enough circulation? my pump is about 500gph in a tall 180g. and where should i postion the pipes?

 

[maelv]

You will definitely need more circulation in that tank. I had a mag 18 (1800 gph) as my return pump and a Seio 820....and felt I didn't have enough flow in my tank....
If you use the two as you suggested one return / one overflow and then take the third and make it an overflow, you could get away with plumbing that over the top and not having any powerheads, but you have you fork out the cash for a decent pump.....
There are so many things you can do....I am no pro here, so I am sure someone will chime in shortly and correct my errors in thinking here....good luck and welcome to the site ibranny....
I will most likely be drilling 5 holes in the back of my 220 when I get to San Antonio because I am going to install a closed loop.