Hi all, I have high tall tanks because I keep seahorses. I am always trying to find ways to use some of that vertical open space. In my last tank, a 56 gallon column I tried a tiered approach and really liked it. I used my largest, most dense rocks for the retaining wall. Then I just poured the sand behind them. I had to use smaller rubble rock to plug leaks but it works pretty well. So my sand bed is 2 distinct heights: the ssb is about an inch while the dsb is probably 7". I will add some photos.