I have heard about using sponges...but I have had ok luck with 'extended release' using a paper towel folded up to a strip. I am using two at a time, and changing them out - one every two days on alternating days. That way, there is always something with moisture in there - doesnt get too high and doesnt go all the way dry either. Cant swear by it as this is only my second try - but its an idea.