I doubt it is anything they did to the water (chloramine) because I do weekly water changes on all my tanks on the same days and of probably close to 100 fish he's the only one that has an issue. With him breathing hard he's opening his mouth wider open so I was able to get a flashlight and actually shine it in his mouth when he was at the front of the glass and look inside. There doesn't seem to be any signs of any lump or even redness inside his mouth/gills. So whatever it is looks to be right at the edge but on the outside of his gills. I know this sounds a bit weird, but do you think maybe he could have got between the heater and glass and actually burned himself from the heater? there's about a 1" space between the heater & glass. I know my oscar did that one time on his tail when I moved his heater to a spot he wasn't use to it being.