Whats wrong with my betta :( He was fine just hours ago

[svtcontour]

Hi guys, I picked up an apple snail today and put it in my tank and until just a couple hours ago, my betta was fine (he was the only inhabitant). I see now a whitish patch on his head. He behaves just fine but I'm trying to figure out if the patch is a disease, heater burn or slime from the snail - maybe he was checking out the snail and got some slime on his head...dont know.

Can anyone take a look and see? Can anything go from nothing to this size in a matter of a couple hours if it was an illness?

Much appreciated.

 

[Lupin]

I don't believe snails carry diseases that would directly affect the fish. Captive bred ones shouldn't pose too much threat compared to the wild specimens. It seems to me the situation was coincidental to the introduction of the snail. It looks like bacterial infection to me. What decorations do you have? What are your water parameters?