It is hard to say what exactly the issue is. My guess is prolonged toxin exposure and a shock when added to a clean system at your place OR chytrid fungus. You will know in a few weeks if it is the latter of the two as your other frogs were exposed long enough to be infected. The desire to escape the water, the floating, lifelessness, and the torn skin have me fearing it may well be chytrid. I had 2 devastating bouts with it in past years. All of my losses were new colonies in the quarantine phase though.