I read about your one tadpole that died, the one that was smaller than the rest. I have about 60 wood frog tadpoles, and I noticed that two of them did not develop at the normal speed, they were kind of like "runts" of the litter, and they died. I guess that some of them do not survive, no matter what care we give them. It doesn't sound like it was your fault, just a kind of natural selection. Good luck with your other guys, may they eat well and prosper!