Looks great! The only thing I would do is take that large rock on top of the right pile (the one that's pretty much in the dead centre of the tank) and move it across to the right, in front of the column. This will open up the centre of the tank, make the right pile not so even with the left, and obscure some of the straight column which I think looks a little unnatural, like a pedestal. With a rock in front of it the pedestal look won't be so apparent. Awesome job!