my betta fighting fsh

Question
My tank has been set up  for about a year.
My tank is
My fish is a Betta Fighting Fish.
2 fish in one tank with a divider.
The type of filter is charcoal.
I used to put in ph, but i don't have any left.
I change the water once a month.
All the water.
One of my fish has a large, unusual, growth bubble(underneath its belly, below its mouth)
I noticed the bubble 3 weeks ago and its getting bigger.
The fish is eating and swimming well.  Is the fish pregnant or is it sick?

Answer
Hi Kathy;

Since he is eating and acting well I don't suspect infection. He may be constipated or he has a benign (non-cancerous)tumor. There isn't anything you can do for a tumor but you could treat for constipation and see how it goes. Here is a link to info about it;

http://www.petfish.net/kb/entry/12/332/

At Your Service;
Chris Robbins