I remember your water was like 70 before. I would not unplug the heater. I did suggest at the time of purchase you get a larger tank and an adjustable heater to keep it an appropriate temp, but 82 is better than 70
Your link doesn't work. I just go to the main page.
I would get the ph and gh of your original water tested along with what you are using now and compare. He may not like the shift. He could be shedding his slime coat in response to the shift, in response to the disease, or possibly a combination of the two is causing this large stress response.
ETA: I checked the url of the link and it looks like you are asking about BettaFix? That won't help anything. http://www.petco.com/product/10673/A...sultRedirect=1
If you were going to add a med I would use Kanaplex, Maracyn Plus or Furan 2 - diluted for the 1.5g since each full dose treats much larger container.