The customer service for coralife is GREAT!! Give em a call, they'll be happy to help! I had to twice, once for a broken part and they sent another one right out! And the second time was the initial set up, so frustrating! I got my skimmer in the fuge also, they told me to take some of the water out so the water line is right at the bottom of the diffuser & the pump 3-4 inches in the water. The tricky thing is that the tube can only be in the box 1 inch, so more than likely u'll have to cut it, and the black foamie on top (in the bubble box) has to be all the way level with the top of the box.
I hope this helps!! I know how frustrating it is!! Good luck!