You should be ok running an extreme in 7 inches of water, but I would simply raise your sump level 1 inch. That should be no big deal to do. Just add some water and add a bit more salt. I would go with an msx 160 over an octopus extreme 160 because although they are basicaly the same skimmer, the msx has two advantages. Its included pinwheel is better than the octopus and the sicce pump is machined unlike the octopus so as to give you a bit better performance. Plus, the msx has a much smaller footprint than the octopus extreme which in your situation is of great benefit. These skimmers will give you substantially better performance that the nw series from octopus because they have wider plumbing and a much better pump. I owned the new 2009 NW 150 for about 1 week, and I sold it because although it worked well, it just did not have enough capacity for my system and bought the msx 160. Moroever, you further can improve the performance of the msx and octopus extreme skimmers by buying an additional large ATB purple pinwheel ($30 usd). I just added the ATB pinwheel to my msx 160, and it really does greatly further improve performance.
