Using distilled water probably contributed to issue. Distilled water has nothing in it; no minerals whatsoever. So when frog takes a bath... the minerals in the frog's body move through it's skin into the distilled water to "balance" things out. Obviously; that ain't good for the frog.
Recommend use dechlorinated tap (Seachem Prime or ExoTerra Aquatize) unless you know what is exactly inside those Spring Water bottles. More on that in here: http://www.frogforum.net/vivarium-te...hing-else.html.
I personally drink spring water right from a spring. There's Artesian wells up here that we utilize on a regular basis. Bring your own bottle, fill them up, drive off.
I have a frog. She's fat and green. Her name is Gertrude, because she is fat and green.