[sweetbourget]

My dad is getting a 235 corner and already has a mag drive 18 and was wondering if he should get another one to run with the one he already has or just get a bigger pump by itself. He will be running them from a refugim under the tank in the cabinet. about 6 foot of hose to the tank from the pumps.

[NATIVEVAMAN]

For a tank with soft coral 20x the tank flow.For hard coral 30X.

[pogodzib]

You also need to remember that you can only push so much water through the overflow pipes, so having one large pump that pushes 20-30x the tank volume through your sump will not work, unless you have extremely large overflow pipes, and even then it won't be your best option.

[sweetbourget]

so if her were to get another 18 he will be pumping about 2500gph because of the height. Is that to much.

[NATIVEVAMAN]

In order to support that kind of flow I believe you would need at least a 2 inch and maybe a 2.5 inch return line.

[pogodzib]

Depends on your overflow size. The max gph that a 3/4" ID hole/pipe can flow is approx. 350gph, 1"=600gph, 1.25"=900gph, 1.5"=1300gph. NOTE: This is the MAX amount of flow. You also need to take into account that you may as some point end up with something partially plugging a pipe and the inside of your bulkhead is probably smaller than your pipe, so you need to computed it on that size. I like to know that if one of my overflow pipes is plugged, the other one can handle it's flow by itself.