1st the Return: Put a T on your return pipe, the straight end going up to the display tank and the T end going to a valve, direct the valved end back into the sump. It depends on how much return water you need, sometimes I have found it to work well if I redirect it to the skimmer end of the sump and let the water go back through the fuge a second time. Other installs the water cant get back to the return end of the sump quick enough, so I have directed it in to the reuturn end. Takes some trial and error. The valve will act as a throttle to controll the amount of water going up to the tank.

2nd Skimmer: Is the skimmer new? check the end that the air hose connect into the skimmer, some times is gets plugged with salt creap or other objects. I use a cut up coat hanger to clean the air hole out.