Need some ideas how to plumb 500gal

[Lucas&kim]

I have a custom 500 gal aquarium with 8 holes already drilled in the bottom of the tank. 4 holes are in the built in overflow and the other 4 holes are in the display portion.
The 4 holes in the display are 1"
The overflow has two 1" and two 3/4 holes.
I'm assuming this tank was built custom for saltwater. The problem I'm running into is I wanna use the overflow as the only drain, but I can't get enough turnover.

 

[Lucas&kim]

Overflow

 

[Lucas&kim]

Inside overflow

 

[Lucas&kim]

Display portion

 

[Niners4952]

understand the overflow part but where exactly are the display tank holes

 

[Lucas&kim]

understand the overflow part but where exactly are the display tank holes

There are 3 pictures. The last picture shows 4 holes on a pvc bottom that's the display portion.

 

[TRENT]

Personally I would cap off the 4 holes in the display area. Put sand over it and you'll never notice. Then use the holes in the overflow box for return and drain.

 

[Niners4952]

Still hard to see where the holes are in pic 3 add another pic farther away with tank in same position

 

[Lucas&kim]

 

[Lucas&kim]