How many gph do I need for my return pump?
 

My tank is about 30 gallons. My sump tank 3ft below my tank. I have 2 Aquaclear powerhead 301s for water movement at the top. So how many GPH do I need to have at 3ft in order to have a return pump that works smoothly?
I've heard there is a calculator online for this, but I haven't been able to find any links to it.

what size overflow do you have?

Unfortunetly I'm not too sure what you mean by what size over flow I have. I built the entire tank including overflow, so there's no real specifications.
it's a triangular middle over flow with two edges 4 inches in length, with a 1 inch hole.

That would be what I wanted. Depending on plumbing, you can probably get 500gph thru that. A MAG 5 would be a good pump for this.

okay thats exactly what I wanted to know. I just bought a mag 7 so I'll be using that. For future reference, how did you know that a mag 5 would work?

Experience. I had a similar setup once, and used a MAG 7 witha valve slightly closed.

Thanks. I'm good to go now.