How do you feed your frogs? Since I started bowl feeding mine, my frogs pretty much never touch the substrate in the tank....and yet the glass is still dirty. I could wash it every day without them even getting substrate on it, it's just dirty from them hopping all over it. Auto misters will work for humidity, but will they keep it level? I could see some extreme highs and lows without any substrate to absorb and balance it. Do you not have any live plants? If not, I'd consider getting some as it'd make for a really nice environment in the tank for your frogs. Half the fun for me is having a beautiful planted vivarium. At the very least, I'd use some paper towels in the bottom.