FYI, this would be my first saltwater set up. I bought this custom 100 gal
tank for $40 on CL
. Haha! ...anyways, I think it was set up as a fish only with an under gravel. Found a false bottom in the cabinet. The base is only 15" wide so this may be sufficient with some power heads on the side. ?. It also goes to a canister before the pump so it's not relying fully on the gravel to filter. Everybody seems to like the idea of an overflow so I doodled some schematics.
This design would utilize the predrilled hole that's all ready there. It's half inch glass and I don't want to drill it myself. The return line is inline through the intake so I'd either have to re-plumb the whole thing and place the return elsewhere, or drill the overflow wall and put the existing one through it with a rotating head to cap it off.