i am not a salty but i am suprised none has helped u yet. i think what u want to do is run one pump in the refugium(this is going under the tank right?) if u run 2 pumps u take the chance of one overpowering the other and overflowing your refuge. if u only have one it will pull the water through the intake aswell as push it out the outtake. i think. try posting in the begginner forum on the salty side and hope the mods dont pull it down here.