I went through this last winter and now into this spring. Same story. Rescued 12 from troughs before freezing, lost 2, both of which were under care of Veterinarian who prescribed Flagyl and Panacur. Autopsy indicated a high degree of bacteria in one frog, possible from time little guy was a tadpole. Also possible the bacteria was in the live feed, some of which I took from the yard. Or I might have kept vivarium too moist, accelerating bacteria growth. Vet said no amount of cleaning would rid vivarium of bacteria, so I didn't break it down. He must have been right because remaining 10 are healthy, ready to be released next month. Some losses are expected due to internal parasites that have been with the frogs since tads. The Panacur and Flagyl helped, I guess; but if I had to do it again, I don't know that I would have subjected the remaining frogs to those medical baths. I will continue with Lymnozyme probiotic baths as long as I have the two I have decided to keep. It sounds like you are doing everything right. All living things are born with time-bombs that eventually get us in the end. It's just hard to lose a little friend seemingly too soon.