travis said:you could have used thinner rock like slate instead. it would weigh a lot less and take up less space.
I thought about slate but I didn't like the way it looked stacked. IMO, it didn't give "natural" look. I wanted rocks to resemble boulders. Once my fish reach their larger size, I wanted the rocks to dwarf them. And Weight wasn't an issue. I had reinforced the bench with 2x4's and spaced them 16 inches apart, attaching each 2x4 to each stud of the wall. The whole bench is on a concrete slab in my garage.
Again, once my fish gets bigger, I will be taking rocks out to make space. Remember, it's only about 200 lbs of rock on the top of the subrate and the rest is makes up the floor.