To much bleach?
Yes.
Well we figured out already he didn't soak it in dechlor water after, so I think that was the problem. I've never measured the bleach when I do my purigen personally, it's the dechlor step that's so important!
Agreed to a point. The amount of chlorine present was way higher than needed or prescribed so the amount of dechlor needed would be even higher. I hate to admit it, but I've forgotten to dechlor a tank during a water change and while they die, they don't die that quickly. For the amount of chlorine used, I would have soaked, resoaked, and let it air out to gas anything else off. Not that I would be using it in the first place....