For expanding the substrate you want to use declorinated tap or spring water, not sure if you have to add declorinator to the spring water but I do just in case. Distilled water has no minerals or anything in it so it draws these minerals that it doesn't have out of the frog which will equal a sick frog. Its only good for misting and foggers, it has nothing in it so when you spray it on the glass and plants it doesn't leave calcium buildup and spots on it. For the question in your other thread yes you will need to change out that substrate, the clorine and other bad things in it will give your frog toxed out syndrome, this is were your frog will swell up like a balloon and stop eating and if not caught fast enough could lead to death. Hope this helped a bit.