Thanks everyone for the insights. I have begun using a water conditioner, and while I have it, I may as well treat the water for all my animals. My next step is to quarantine all of my new frogs. Rather than tear down my existing setup (it took years to grow) I am going to try and fit it for an external filter that can maintain the small sump at the at the bottom of the tank. I realize I'm not at that level with this species, but unless I'm mistaken, a dish of water may be too small for breeding purposes. Meantime, in reference to the possibility that pathogens rather than chlorine was the cause of death, I am wondering if the existing tank, if left vacant (of animals) for several months, would once again be safe to use, or if pathogens are likely to be species-specific, and the vivarium could be safely used for an unrelated species of animal. Will keep you posted on my last two greys.