which mag are you talking about? If the pump is 4ft below the return exhaust in the main tank, then you have 4ft of head (resistance that really slows down the flow), and it has been said that for each 90* elbow in your plumbing (from the pump to the return inside the tank) you need to add one foot. There are alot of sites that has a chart on them to let you know what the flow rate is after so much head pressure.. one that I use is
Mag Drive Flow Rate vs. Pump Height
(I hope mods don't mind, since SWF.com doesn't sell Mag drives)
If your overflow is 300gph, then a pump rated at 300gph before head pressure will work, maybe not as efficiently as a stronger pump would.. but it won't overflow the tank. The overflow can only drop as much water as is pushed into the tank, so a smaller flow rate than 300gph will work, but you might want a bigger pump and a flow valve on the return line to underdrive the pump some so it won't overflow the tank if it has a little too much power than your overflow can handle.
Just consider you start out with 4' of head with the height, then you probably have two 90degree elbows to U-turn it into the tank, and you might have some 45* or 90* elbows to get it from the sump out of the stand so that it can go up to the tank.
So with that considered, you might have 5-6 or more feet of head.
but hey I'm no expert either.. heh
I know that my mag9.5 is supposed to flow at 800gph at 4' of head, which I have along with 2 90* elbows, and I still had to underdrive it slightly so the overflow could keep up. The overflow is LifeReef rated at 700gph. I thought the two 90* elbows would slow down the flow enough from the pump, but not the case, I had to put a flow valve inline and turn it down slightly.
hope that helps.. sorry for the novel
cordell
