Water Displacement & Required Aquarium Thickness?
 

Would an aquarium filled only with water need the same acrylic thickness as an aquarium (of the same height & length) filled with water and rocks? I think (based upon reviewing online calculators) the answer is "yes"... they would both need the same acrylic thickness (or glass thickness).

However, I am not sure. An aquarium filled also with rocks would have less water "pressing" against the aquarium. I would think that this would mean less water pressure on the acrylic/glass. Still, the online aquarium thickness calculators do not include aquarium width as a component and an aquarium with less width would also have less water "pressing" against the aquarium. Perhaps the rocks don't alter the downward pressure of the water?

As background, I really like rimless drop off aquariums. I am wondering about building a different type drop off aquarium that would provide more drop offs. In effect, a smaller aquarium glued upside down to the bottom of a larger aquarium in order to provide four "drop offs".

I suspect that such a design (even though it would have much less water) would not change the thickness requirements of the acrylic (or glass) but I am wondering about the view of others with more expertise.
Thanks