yeah just be SURE to clean the sponges consistently like marla said. they are serious breeding grounds for mold and bacteria--one reason why i don't use a sponge to wash dishes. who wants to wash their dishes with a wet, bacteria filled mold haven? blech. on that note, i use reptile moss in my humid hide--do you think that stuff would grow a lot of bacteria too or is it safer because it is less porous?