jawwad the taller you go the stronger the support needs to be.
I got away with 1/2" solid acrylic rods, my rock stacks were just 20" high.
any taller and I would go with a thicker rod or switch to a fiberglass rod.
yes the heavy rocks go on the bottom, some of the towers are getting help leaning into a corner, but for the most part if you balance them right they are very stable. I gave them a shaking and none of them fell over.
i shook the pillars in the tank, by shaking i mean i pushed on them with way more force a fish or invert would be able to give them and they were rock solid
I got the rods at canal plastics, $6.95 for 6'
the rods are almost completly hidden, the spots that do show will either turn purple, or will have coral grow in front of them. they are very small spaces though and do not jump out at you when looking at the tank.
I love everything about it, the way it breaks the surface, the nooks and crannies, the overhangs......just looks so natural. I'm already envisioning my next tank
I figure on just pouring water over the rocks as needed.
So far the rocks seem to stay pretty moist up top. There's always a snail
or two hanging out on one of them. I wonder what they think being
able to climb out the water now