Yes, they do suggest the Mag 7, and that's what I have, but many people overdrive the skimmer (using a ball valve to control flow) using the Mag 9 or the Eheim 1262 and report having a lot of success. The Eheim is a better pump than the Mag 9 and runs a lot cooler. You'll notice that the Mag 7 gets very warm, which transfer heat to your tank.
Also, regarding the elbow, the AquaC manual discusses the use of an elbow/T.
"Important! If you decide to add pipe/fittings to the gate valve to prevent splashing and/or cut back on the noise of the water returning to the sump, be aware that you must install a “siphon break†in order to ensure proper function. A siphon break will let some air into the drain line, which prevents it from sucking water out of the skimmer faster than It would normally fall due to gravity. If you plumb your skimmer so that the returning water exits a pipe below the sump level, a siphon break is critical to achieve good performance. You can add a siphon break to the exit plumbing by drilling a ¼†hole in the PVC, or by using a “tee†fitting in place of a 90 degree elbow. Leave one end of the tee facing upwards and open to air flow."
Also, the guys at AquaC are very helpful--e-mail them with any questions.
