that's terrible! How deep was the water? They can drown if its to deep. Other than that I don't know what went wrong. I guess just describe everything you did to take care of it so i can make a better guess at what went wrong. These guys are fairly hardy and can often show no signs of sickness until they're gone. They can absorb harmful things through their skin, so if you had been handling him a lot with out washing your hands well, then that could be it.(don't use soaps or cleaners) I'm not saying it was you, but I'd hate to see it happen again. Sorry for your loss.