I set up a 40 gallon breeder tank using the above as substrate. No sand or gravel. I thought it would be easier to clean. Well, it is not. Lots of stuff (don't know what it is..clumps of poop from two fish with food) gathers under and around the rocks. I have to manually move them around to suck up the stuff. How about just piling up the rocks in a couple places and leaving the rest as plain glass? I would then just suck around the piles and just deconstruct the piles once in a while. Any thoughts? The river rocks are 3-5 inch semi flat colored stones.