Blister on Calico Fantail

Question
Hi Stephanie,
I have a calico fantail (Sinatra) that I have had since October. He has recently
developed a blister just above his mouth. He has had two in the past couple
weeks and its starting to worry me. I notice them when I come home after
being gone on the weekends (he is being taken care of by my roommates
when I'm away). The blister sometimes appears bloody. He hangs around the
top of the bowl a lot and has done that since I've had him. He is in a one
gallon bowl right now, which is probably not good, but he is the only fish.
What could the blister be?

Answer
Dear Anna,

  A bowl is terribly insufficient.  He needs at least a five gallon tank.  I would suggest changing half the water in the bowl once a week if not twice.  These are probably due to bad water conditions.  Make sure to use a water conditioner.