Can you tell me what is wrong with my betta fish?

[j.thompson05]

My male betta fish seems to have something wrong with his gill, or the fin near his gill, on his left side. At first I thought he had some of his pellet food stuck in his gill, but after several closer looks overs the past couple of days, it looks more like something (maybe the joint where his fin connects to his body?) is swollen. Before I noticed it, my boyfriend and I were checking out his home, and he came swimming up, flaring his fins like he was really angry or something. My first thought was he was reacting my boyfriend, who doesn't visit his tank as much as I do (but I don't think fish are that complex). When he turned, that's when I noticed his condition. I assumed he was flaring his gills to try and dislodge it, but now it seems more likely he's flaring just from sheer annoyance. I wish I could get a good picture of his left side, so that whoever reads my question would be able to see exactly what is going on. I added a little bit more freshwater aquarium salt, which is supposed to improve gill function. Is it possible the salt is what's causing the problem? I didn't add an extreme amount, just what the directions specified when I first put it in, and then a tiny, tiny amount more yesterday. Sorry for all the rambling. I'm just trying to give as much detail as I can. If anyone knows what is wrong with my fish, and what (if anything) i can do to help, please let me know. Thanks!
I checked out the link to that website- it seems he has a minor case of fin rot (which he had when I got him, but I didn't recognize it at that time), but it didn't mention anything about his "tumor". I tried to get a picture, but he didn't like the camera. The best way I can describe it: imagine a "bead" that looks like a small food pellet, only somewhat metallic goldish. It's right at the base of the gill fin.
Oh, and Delias, his name is Edmund. Thanks!