Has anyone used foam to make rocks and caves? I am trying to plan aquascaping for my tank I am setting up and was going to create sturdy caves and ledges using the concrete live rock instuctions on www.garf.org (yes-they are fully cured, and no-they dont use regular instant concrete mix.) They explain how to encourage coraline growth and algae to "make" live rocks, but I realized I would be making butt-burn heaven for my cuttles. Could I use blocks of foam-not styrofoam, but prefilter type foam and carve them to rocks and caves? I have seen from foam in my sumps that they would look like rocks. If they jetted into them-it would be a big pillow. These caves will have to be big to shelter a 15" cuttle and I wanted multiple hiding spots. Foam here is available and inexpensive compared to base rock. Then I started thinking would a layer of foam under the sand bed help make room for anaerobic nitrifying bacteria? Kind of like media for a deep sand bed? This all seems too easy, show me the error of my ways.