pump size

[I like shrooms:)]

im working on a 30 gal sump for a 75. i was just wondering what size pump would be recomended. im worried about haveing microbubbles. i read somewere that if you have to big of a pump it would cause microbubbles. i realize that the bubbles would be because the pump is to big(allowing air in). but i want a big pump to get circulation in the tank. would it work if i just used a big pump with 1" pvc then when it gets up to the tank cut it down to 1/2" pvc to make it pressurized. slowing down the flow of the water but giveing it force at the end points?

[Tangster]

A mag 9.5 max and a mag 7 min.