What size return pump do I need?

[Meric]

I am currently setting up a sump for my 125 Gallon Tank. The tank is 72 X 18 X 22 on a 30" Stand. The overall height from the bottom of the sump to the top of the tank is 5'. I am interested in putting (4) .5" returns into the tank and having one 1200GPH Overflow box on the tank.

My question is how do I determine what size pump I need? I was thinking of getting a Mag 12 or Dolphin 1200 both submersible, but with 4 returns @ 5' will it have enough power to create enough tank turnover?

Both pumps have .75" Return that I would reduce to .5" after 3', but I will also have some bends and turns in the return pipe that I am making with PVC.

The sump will house my protien skimmer, heaters, and any resins or carbon that I may want to use. It will also have my bubble baffle.

If it matters the sump is 24 X 16 X 16 (25 Gallon)

Thanks in advance for any help.

[Poseidon]

If you are going to have a lot of el's get the Mag 18. And remember when you reduce to 1/2 it will increase velocity, but not the volume of water you are moving. I think the best current is lower velocity but higher volume. That is created by using larger diameter pipe. I use 1" on my mag 12 through just 1 return in the opposite end of my tank. Then I used PH to create more random current in the tank itself. My .02