First you get tile grout, whatever color you want, then you get styrofoam, or a different type of foam that does not break as easily(cant remember the name).
Steps:
-Cut out shapes of rock ledges you want
-hot glue them, onto a styrofoam sheet that fits the back of the tank
-mix grout according to the directions on bag.
-use a painbrush and brush a light coat of grout on all the foam
- do a second layer of grout on the foam
-do a thrid and thicker layer of grout on the foam.
-let it air out.
That is a very nice display case and i love how you placed slate on the bottom. Yes i guess alot of people do have that same log. It works great and looks pretty nice as well. Nice tub as well and beautiful females. Looks like you have some calcium dust ALL over your tub floor. lol