Angelfish with bubble

Question
My angelfish has a cream-colored bubble of some sort hanging from his anus.  It appeared yesterday and has not changed since I noticed it.  His body is fuller/slightly swollen, I noticed that a couple of days ago.  He is eating and swimming around in his usual way.  He's in a 55 gallon planted tank with community-type fish that has been established for 3 years.  Any idea what is wrong with him and how to treat him?   Thanks,    Susan

Answer
Hi Susan,
This seems to be an internal bacterial infection. Usually it is very difficult to feed and in later stages the fish will refuse to eat.Soak some live tubifex worms or black mosquito larvae in a solution of 10 ml of liquid Flagyl to 200 ml of water for about one hour. Then feed the worms or wrigglers to the fish. This treatment can be repeated every 2 to 3 days for 10 days.

Hope this helps.
Chloe.