enough flow?

[JGoslee]

I have a 20gal long that I want to drill. I want to drill a 1" drain in the center and 2 - 3/4" returns in each corner. There will be 3' of head. I will be using a mag7 or mag9.5. Will there be enough flow coming out of the returns? I wanted 2 returns to avoid putting in a closed loop. Would it be better to have only one return and a closed loop?
This tank will be for sps and clams. Thanks

[JGoslee]

ttt

[Lights Are Bright]

It should be enough, but it also depends on your rock placement and stuff. A mag 9.5 should be plenty and if you want more, you can always add a powerhead.