I was wondering how full my Nanocube back three chambers should be...as they are all full to the top, and I am not sure if that is normal.

Are you using the optional surface skimmer that comes with the DX? I use the divider between chambers 2 and 3 as my fill line and I have the surface skimmer set up so that the water is exactly at the bottom edge of the trim.

I do have that. My water line is near the top of the back of the tank and all chambers are equally full....so I should lower the line some?

edit

That makes sense. I will lower the water when I get home