I wanted to add another tidbit of information to this thread. One thing that the guys at Aquatic Reef Systems did on my unit was add an adjustable restricting valve to the waste line. I don't know if the AquaFX systems have this, but you could easily add one (Lowe's sells them).

This allows you to tweak the amount of waste water. By restricting the waste water flow, you can signficantly increase the output. The typical units are designed with a "best guess" restriction. You need a TDS meter to make sure you are still getting good water out, though.