my betta has a weird mark on his face

Question
I bought a betta fish, Bowie, about a week ago.  I have him in a little over a half-gallon bowl with plastic rocks at the bottom.  He hasn't been eating very much, hanging out mostly at the bottom of the tank, and a few days ago I noticed a white area on the left side of his face that wasn't there before.  His water felt pretty cold to the touch, so I put a lamp over his bowl.  He's much more active now than he was before.  Could it be that his water isn't warm enough, or might there be another reason for the white area?  It doesn't seem to be affecting him, but I am still worried.  

Answer
Hi Meg;

It could be fungus or bacteria that attacked his weak body when the water was cold. You will need to get an aquarium thermometer so you know exactly what the temp is. Keep it up to 80 or 82.

If the spot gets larger he may need some medicine. Here is a great site with info on treating betta illnesses;

http://www.bettatalk.com/betta_diseases.htm

At Your Service;
Chris Robbins