Don't do it. I have an identical set up and, though it took me a while, my 9.5 is the right pump. The 7 is too weak in my opinion. I had one and forked out $90 for the 9.5 because my foam column never reached the top of the reaction cylinder.
Also,
1.a)make sure the inside of the "black box" is free of calcium and other deposits. It's worth it to dis-engage the entire unit and scrub it out with warm soapy water. Take your time doing this as "rough" surfaces like calcum deposits cause tiny bubbles to form into bigger bubbles before they get to the reaction chamber and severly interfere with the skimmer's ability to skim.
1. b)make sure there is no back-flow pressure on the water flowing back into your sump.
2. use a large rubberband (a rubberband 1/4" wide and 4-6" in diameter) to prevent skimmate from "spitting" out the interface between reaction cylinder and collection cup. (I haven't actually called Aqua C to ask if they have a washer that more precisly reduces the tolerance, but if you have the time be my guest and PM me with the results)
3.turn you air intake way down, until the level in the cylinder is just boiling at the top of the "black box." It may not immediately produce a foammy columb.
4.leave it alone for 24 hours and check it 6 hours after your last feeding.
I write this to you because it took me weeks to figure out how to use my 180 but I will tell you it is a GREAT skimmer with the pump you have if you set it up correctly.
Keep me posted.
-John