I think you need WAY more rock. Your wall is going to be exteemely bouyant with that rock to foam ratio. Not to mention that, at least IMHO, the more rock, the better it looks, and the easier to attach frags.
I was not sure about the rock I put in it because I will still have TONS of rock in front of the wall so I didn't want to waste too much on the wall. this is on a 8ft 300g too so it would have taken a lot of rock. I am almost done with the canopy then when I get them siliconed in I will snap some finished pics. hopefully it will look nice at the end