A larger fish will easily root down to a couple of inches or so of coarse gravel, perhaps deeper in finer gravel or sand, I would assume. Don't know about the snail thing as never had any in my tanks, never bothered to have any live vegetation either as it would be uprooted in short order with these fish. As far as the behavior of holding on to pebbles in the process, I assumed it might be to clean the algae off the rocks and pebbles?
