With my woodfrog tads, i kept them in the pond water only. i would get new water every few days, and pour it through a fine net a few times to filter out debris and small insects. I have been doing this for about 2 weeks now and only one death out of about 45-50. another possibility is oxygenation; even goldfish will die if kept in a tank of un-oxygenated water. a small, slow airstone could help, or just change half the water daily with new filtered pond water if possible. Also make sure the container you put them in is clean, no soap residue.