I cut some large diameter ABS pipe into sections to support several large pieces of live rock. Drilled random holes in the sides for circulation. I should have siliconed them on to the bottom glass though, since they've shifted a bit on me while I was messing around rearranging stuff. Next time I start up a tank, I'll likely do the same or just cut semicircular sections as shown in the photo below. By using sections of ABS like this, you have more flexibility as to placement and the entire bottom doesn't have to be covered as when you use eggcrate, allowing for better access and circulation. Another advantage is you can customize the height and profile of the ABS pieces to better suit the shape of a particular rock.
