I've got a number of medium rocks from my area in the tank with my firebellieds. I rinsed off the dirt (and some kind of slime mold) and boiled them for 5 minutes. No reason to waste gas/electricity boiling small-medium rocks. Going to revise their setup next Friday (currently just water with rocks above the water level. Thinking to do like my 40G breeder that my bullfrogs live in and silicone in an elevated land area. Mine spend most of their time in the water, so ~40% more water space while still having land space (and not just blowing money on a larger aquarium) seems ideal.