Bahamut, Tiki ...thank you both for your help thusfar.
I decided to take your advice for the water change. I put him a temporary mini-tank (the plastic container he came in), to see how he reacts to the following:
I put just the tiniest bit of tapwater (like 1/5 of the container), and the tiniest bit of treatment/conditioner for it, and the rest, the same bottled water. I didn't move him back into his regular tank yet because I'm not sure how to handle that water. Also I want to see his reaction to tap water. Also I did not put the plant in the little receptacle, but I did cut it way back and rinse it off so I can put it back into the tank.
I plan on having a portion of tap water in the tank, but how quickly/often should I adapt him to tap water?
He is still a little distressed/darty. He definitely was having trouble breathing in that other water - he is breathing pretty heavily now.