some comments though to ur system bro.... try to minimize the angles in ur return pipe, this will drastically lessen the pressure of ur water to tank...
also, try to maintain the "U" tube of ur overflow box; there should not be any air in it.. remove it by siphon....
was worried that 300gph might not be enough....if not, will pass u the 800gph instead... anyway, will arrange w u when i can pass the durso
cheers!