I am so sorry about your losses. I know what it feels like when it seems you do everything "right" and then there is "unexplained" loss. I, also have raised Taricha granulosa, and I have experienced all the challenges of raising them from eggs. Though I have had some success raising a few to adulthood, I also have had some"unexplained" losses along the way. One thought that comes to mind: hidden disease in the tank. Sometimes, even the cleanest tanks can carry disease and bacterial colonies hidden in the plants and rocks that can transfer to cleanly added water again ( if rocks etc are not cleaned also ). I have had fish epidemics spread this way. Also, another thought: your juveniles might be going through life-cycle related changes in their needs. I just know,my juvenile Taricha seem to really want to become "land phase" after metamorphasis. I have tried keeping them aquatic... but they seem to really "want" to get out of water and live in rocks and leaves ( they try to climb on up everything!). Their skin gets really rough and bumpy like their hormonal state is "pulling them" to the land. However, later in life, (about 18 to 24 months old ) my Taricha seem to accept being aquatic again. ( I always like this because aquatic is an easier set-up!) Anyway, I just wonder if your juvenile Taricha might thrive better in a land set-up for now? Just some thoughts...
Please know I am rooting for you and your little guys! ( I love the species)
Jane