I'm one of those people who had a betta with a tumour. I assume it was cancer. Poor little guy, he was acting completely normal and active with a great appetite to match up until the day he died. Not knowing what to do, I tried multiple medications to get rid of the tumour and I'm sure that shortened his lifespan. None of the meds helped to cure it. However, the tumour didn't look like the swelling that your fish has (my fish had a completely smooth circular lump on his side that continued to grow outwards as time passed), Alison, so I'd suggest contacting OldFishLady for advice.
If I were you, I'd stop using the Bettafix until we can establish what that swelling on him actually is. All of the medications with the -fix at the ends of their names contain tea tree oil, which damages a betta's labyrinth organ. As you probably know, they are not like other fish and do not take the majority of their oxygen with their gills. Without the labyrinth organ, they cannot breathe air at the surface, and will eventually suffocate.
Petco guy is partially right, partially wrong. If you want to go through cycling your tank and have a filter, than the two 50% changes per week + once a week gravel vac are good. Just keep in mind that in tanks under 5 gallons, keeping a stable cycle can be somewhat difficult. If your tank is unfiltered, you'll have to continue with the 100% changes. 100% changes are stressful to a fish, but not as stressful as ammonia-filled water. You are overfeeding a bit since Hikari Bio-Gold is significantly larger than many mini-pellet brands, so do cut down to 2 or 3 pellets per meal with twice-a-day feedings, but don't reduce to 2 - 3 pellets per day.
Its hard to tell much by the pic...can you try to get a pic of the area with the flash...that might help some to at least see the area in question....
If it is Lymphocystis=the lump generally will appear whitish/pinkish color cluster and being a virus-there is not really a treatment, however, is usually isn't fatal unless it impedes on daily living.
If its a tumor-not a lot can be done either and while some tumors can kill the fish-usually they are slow growing-but it depends on what type it is and location of the growth. Usually a tumor is fatal when it grows large enough to affect internal organs not the tumor itself per se.
It also could be a parasite and treatment can vary on this-usually manual removal with tweezers-but it hard to say if that is what is going on-usually if it is a parasite the Betta will be flashing or trying to rub it off by hitting its body on object in the tank.
Since he is otherwise acting his normal self, eating, swimming, responsive to you...etc......Not really any treatment I would recommend, however, you could try Epsom salt (Not aquarium salt) and see if that would have any effect on the swelling/edema of the lump-It may or may not help-but it won't hurt either.
If you want to try the Epsom salt, since he is otherwise acting okay-I would treat in his tank.
Use a cup to premix and dissolve first-Add Epsom salt 2tsp/gal and just enough hot water to cover-once nearly all dissolved-then add either fresh dechlorinated water or some of his tank water to fill the cup up. Slowly add the dissolved Epsom salt water to his tank over about 30min.
Premix your replacement water to use for water changes in a 1gal jug of dechlorinated water-Add the Epsom salt 2tsp/gal to use for water changes to provide proper dosage. Premixing just makes it easier to maintain the therapeutic dosage when making partial water changes.
I would make every other day 50% water changes with the premixed treatment water for the next 10-14 days. maintain water temp in the 77-78F range during treatment.
If you have a tannin source of either IAL (Indian almond leaf) or naturally dried and fallen from the tree Oak leaf-you can add this to both the tank and the premixed treatment water. The added tannins can help toughen scale/fins as well as the antibacterial/fungal properties.
Thanks for responding! I have printed out your directions, and will try the Epsom Salts. Can this just be Epsom salts that I buy from walmart in the blue bag, or do I need a special epsom salt that is made just for aquarium use? (I have a bag from walmart already).
I will try get a better close up picture and post later.
I haven't noticed if he is rubbing up on anything....he really seems to be acting normally to me. He's never been a super active fish ( he has a big billowy tail, which seems to slow his movement a bit, and he prefers hanging out near the surface mostly), but he can dart around if he wants to. (like if I'm trying to put him in his cup to change the water).
I've had epsom salts in the tank now for 7 days, and I just got the Indian Almond leaves in the mail yesterday from singapore. I put one leaf in the tank, and today the water is light brownish....and smells a little like old laundry. ( is this normal? the smell I mean)...I expected the color, not the scent!
The bump does not look like it's changing though, seems the same size as it was. Bobby is behaving normally still though.
I've been feeding slightly less, only 4 mini betta pellets 2X a day. (I think I was overfeeding a bit).
And I'm doing the 50% water changes every 2 or 3 days, and I got a gravel vac for the gravel.
I also got him a 'floating betta log', which, once he got used to it, has been his favorite place to be.