From what you posted before..
You aren't changing his water enough. Your unfiltered 2.5g should be getting 100% changes every 4 days, and ideally another 50% change at day 2. Only changing a small part every two weeks is going to cause big time issues. Also, unless you keep your house a constant 80-84 degrees he's too cold and it needs a heater.
If you want to feed freeze dried blood worms as an occasional treat that's fine. You should be using a high quality low wheat pellet like Omega One Betta Buffet or New Life Spectrum Betta regularly (4ish on the Omega One and 6-8 on NLS) daily unless you're supplementing with blood worms and with one fast day a week.
What size is your tank? 2.5 GAL
Does your tank have a filter? No
Does your tank have an air stone or other type of aeration? Not sure what that is, he has a floating log he likes to lay in
Is your tank heated? No, it stays warm enough because of the weather outside, its always warm in the room, I check the tanks regularly
What tank mates does your betta fish live with? None
What type of food do you feed your betta fish? Freeze Dried blood worms
How often do you feed your betta fish? Every third day, but he gets pellets in between feedings
How often do you perform a water change? Every week or so I do a 1/3 or 1/2 change, sometimes its every other week but I dont let them get nasty
What percentage of the water do you change when you perform a water change?
What type of additives do you add to the water when you perform a water change? Top Fin dechlorinator
Have you tested your water? If so, what are the following parameters? I have not
Symptoms and Treatment
How has your betta fish's appearance changed? His color has gotten prettier, not really a bad color like a sick fish would, he was in front of a window for a while but he was moved a few weeks ago because of the turtle we got, and since then his main purple color has started going up his back almost like it was supposed to.
How has your betta fish's behavior changed? None
When did you start noticing the symptoms? Today I noticed what looks like a tumor under his little fins below his head in the abdomen area
Have you started treating your fish? If so, how? No, I just noticed this today
Does your fish have any history of being ill? Nope
How old is your fish (approximately)? I think we got him in early fall of 2011 if I remember correctly
He acts pretty normal, I couldnt get a really good picture and Im about to go out for work, but ill keep trying and hopefully have one up by tomorrow... is there anything I can do for him if it is a tumor, or could it just be some kind of disease that can be treated... Id hate to lose him