Turtle experts, please help!!!?

So I have a water turtle, her name is Oscar by the way. :) I am having trouble with cleaning her tank. The hardest thing about it is the little rocks that you put in so the turtle isn't standing on just gl. The rocks seem to collect so much gunk and bacteria and they are the smelliest part about cleaning my tank. And here lately my pet has been keeping me up all hours of the night and then waking me up super early in the morning with her digging around it the pebbles. So what I would like to know is there something else that I could put in her tank (at the bottom) besides pebbles. I want it to be safe for her too. If you have any suggestions please if you could let me know where I could get the stuff from. Thank you for all your help!