Looks like a bacterial infection - probably Columnaris. If you haven't done a water change already within the last few days, do at least 25% change. Remove any charcoal from your filter and treat him with Maracyn 2.
Ideally, you should use Maracyn and Maracyn 2 together for the spectrum of pos. & neg. bacteria. If it were me, I'd treat him with the Maracyn 2 until you can get the other. I don't have any experience with QuickCure so can't speak for that.
Keep us posted on how it goes. I've got one of my own little guys battling some type of bacteria too this week (groan). I'm using Furan-2 bc it works the same as the Maracyn combos but I couldn't find Maracyn in stock and didn't want to wait for a shipment of it.
Good luck. Hope your lil guy is ok.