I posted on tropical fish keeping and no one has any idea what it is so I figured I would come here.
He's in a 2 gallon hex tank that stays in the 80-82 degree area. I've had him in this tank for about 6 months and he's by himself. No filter because it's such a small tank but he gets 25% weekly changes and he does have a heater. He is getting over a swim bladder problem that was my fault I was using flakes and must have over fed him so now he gets one Omega One Betta Pellet every morning and once he can swim normally again he'll get two twice a day.
I didn't see the sore when I fed him yesterday morning around 10am but when I went to do the water test at around 4pm I saw it. The only things I can think of is he got himself on a plant (mine are plastic and because of this incident I have some silk ones on the way for him), or it's a dried out patch from sitting at the surface of the water. It is the highest point on his back and it does sit just above the water and because of the swim bladder he's been at the top a lot. Otherwise I have no idea what this is.
I did give him a dose of API Bettafix and Stress Coat+ shortly after I saw it.
He acts and eats normally and he's even gotten to the point where his swim bladder problem is almost gone. This is the second day he's had his sore and it's only gotten worse but he is still acting normal.
This first picture is from yesterday when I first noticed it and the second is from today.
My friend pointed out that he does look thin but I had cut his feeding way back for almost a week to get his swim bladder to normal again and today he got bumped up to four pellets a day. I'm totally baffled. Google has given me nothing and I would hate to haven gotten him over the swim bladder ordeal only to have this kill him.
I've pretty much decided as long as he's happy I'll keep treating him but if he turns I'm prepared to put him out if his misery too.