Originally Posted by reefbound
I've built my own overflow following directions from Melevsreef.
Would love to see a pic when your done. You might want to confirm this with him but I don't think you'll get much more than 750-800 GPH
though a 1" bulkhead. This would put you at the bottom end of the desired flow rate for your tank with the sump return as your sole source of flow.
The vertical hight is 3'ft 10"inches, I would like to split it so I can have flow on both sides of the tank,And no I have not consider the closed system.
The two pumps I was looking at are the Mag 7 & 9...I was also going to keep the return at 3/4 instead of 1" and the drain down to the sump 1"inch.
A MAG 9 split off will get you about 700-750 GPH
back to the tank (best scenario). So with one overflow, one return pump and two return pipes, I would plan for variables and go with a MAG 1200 or Iwaki MD30RLXT instead and add ball valves to each return. This will allow for the most flow and control so it won't overflow the tank and you won't fall short of what the overflow can handle. Too little flow and you'll lose the siphon, too much and you overflow the tank.