overflow issue

[rock-n-reef]

I bought that tank used. I have no idea what the overflow box is rated for. It’s a tenecor 4’x4’x24” 240 gallon tank that was made before they went out business back then. The outer dimension of the overflow box is 10”x6” but the size of the teeth looks very big. Even at full speed the water level inside the overflow doesn’t rise as well but the water level outside of the overflow in the tank rises to the top of the tank.

That's a nice dimension tank. I would just run that with 900/1000 gph. That's more than enough sump turnover. You can add sufficient internal circulation with powerheads. If it is a dc pump, just run it at half speed rather than throttling it with ball valve.