the black sand and gravel look is starting to really appeal to my eye . . . it's a nice look . . . i might add one plant in each corner, but really your "stone style" is nice. i would not touch it.
awesome!!!!! i wouldnt add any more decor. i love the look you have going on in there. sort of dark but then you have your fish which just stands out in the dark background. definitely leave it like this if i were you.