Now I'm starting my first DIY 3D background for the bottom tank. I've never made one before, but I've been reading all I can on the cichlid sites.
I bought a sheet of blue insulation at Lowes ($10 per 4'x8' sheet by 1" thick). I had to slice & dice it in the parking lot to fit in in my little Hyundai Accent! lol I didn't know insulation was covered in thin plastic - I removed it. Nothing I've read on the sites mentioned it, but I think you probably have to for a tank.
I used the 29 tank as a template, and cut two pieces. One is a solid backing - the bare canvas, if you will. The second piece is for added depth, and to allow me to cut out a shape to accomodate the intake of my HOB.
Next I drew rough rock shapes/directions on the third piece, and cut out the rough shapes into individual smaller shapes. It was much easier for me to carve that way. So I wouldn't forget where things went, I wrote letters on the jigsaw pieces & back to match them up. After I siliconed them down, I went back in some spots and carved even deeper into the sheet below (not the base sheet). I like the depth it gives.
All I ended up using was a steak knife - I have a propane torch and was going to smooth the edges with it, but I like the jagged look. Maybe I'll use the torch a little next time (I have two tanks to do). So this has 3 sheets - one solid base sheet, one middle sheet, and the top sheet that I cut the rocks out of. The little accent pieces I added to the very top are from the scraps left over from carving.
It's all glued up with GE1 silicone, when it hardens I'll tweak the carving. Btw, when I glued the sheets and "rocks" up, I spread the silicone out with a bit of cardboard - so there is 100% contact on all pieces of styro.
next - experimenting with Drylok and quickcrete colorants!