Email the seller and confirm how many gph
the overflow box is rated for. It looks like a single return hose so it's probably around 600 gph
. Then you have to take into account the distance between the placement of your pump and the top of your main tank.
This similiar wet/dry: http://www.aquacon.com/wetdry.html
recommends either a mag 9.5 or a CAP 2200...