The stringy is bacteria from the carbon dosing.Hopefully diatoms. If so, normal for a new tank, and will go away.
But a bit stringy, so not so sure.
You sure you want a wall like that?
Personal aesthetics aside, it can be a pain for flow, cleaning, and so on.
As for the wall, there is room behind it (except at the top) and nothing is glued in so we can restructure in the future. We wanted as much sandbed in the front as possible and kinda tall 'cause our lighting is only 4 x 24 inch t5s and we wanted the top to be flat with room for frag plugs.
We are supposed to clean the rocks?
Cheers! Mark