I'm sorry if this is off topic, but I've noticed here recently a few of the members using foam to keep their pacmans on. I kind-of like that idea better than Eco Earth as it makes me a little paranoid when I go to feed and they ingest it with their food item. I know it's highly digestible, but it still makes me leery. How often do you have to change the foam if kept in a set up like that?