Cardinal tetra seems to have an ulcer or tumor?

See information and photos below - mostly just concerned if I should be using stronger medications or if the main tank needs to be medicated? Any advice is appreciated, thanks.

Tank
What is the water volume of the tank? - 15g
How long has the tank been running? - 9 months
Does it have a filter? - yes
Does it have a heater? - yes
What is the water temperature? - 76F
What is the entire stocking of this tank? (Please list all fish and inverts.) - 2 honey gourami, 8 cardinal tetras, buttload of Malaysian trumpet snails

Maintenance
How often do you change the water? - every 2 weeks
How much of the water do you change? - 25% - 33%
What do you use to treat your water? - prime, excel, flourish
Do you vacuum the substrate or just the water? - substrate

*Parameters - Very Important
Did you cycle your tank before adding fish? - yes
What do you use to test the water? - master test kit
What are your parameters? We need to know the exact numbers, not just “fine” or “safe”.
Ammonia: 0
Nitrite: 0
Nitrate: 10/20
pH: 6.4

Feeding
How often do you feed your fish? - twice daily, skipping meals sometimes
How much do you feed your fish? - try not to feed a lot in one sitting, but enough that everyone can notice and grab some
What brand of food do you feed your fish? - tropical vitality color flakes & north fin bug pro
Do you feed frozen? - no
Do you feed freeze-dried foods? - no

Illness & Symptoms
How long have you had this fish? - 7 months
How long ago did you first notice these symptoms? - 4 months ago
In a few words, can you explain the symptoms? - 2 of the cardinal tetras I noticed in January were bloated / larger than the others - I posted asking for help about one of them in March as it started pineconing. It died 5 days after I noticed the symptoms. I've kept a close eye on the other one since then, and while it's not pineconing its continued to get larger, and just today I noticed it had this white "ulcer" looking thing on it. If you look at it from the top, it is very lopsided on the left side. The right side looks normal.
Have you started any treatment for the illness? - I gave it and another tetra that was looking a little bloated an epsom salt bath maybe a month ago - the other tetra was completely normal the next day, seemed to have no effect on this one. I'm just finishing giving it another one as I'm typing, then I'm going to move it to a quarantine tank with some aquarium salt & an indian almond leaf. I snapped a quick photo just now while moving it out of the salt bath which I'll upload below.
Was your fish physically ill or injured upon purchase? - no
How has its behavior and appearance changed, if at all? - no behaviour change - seems to eat very readily and schools with the others

 

Can't really tell what it is for sure. Not sure how to treat an ulcer. If a tumor, supose it can be removed, though i am sure it would cost way more than it cost, not to mention looks like a big %% of the fish's total mass. Not really anything to do otherwise if a tumor. Try keeping comfy, if he gets too bad and can't do things like eat or move, euthanasia is an option. Otherwise, fish can go quite awhile with a tumor.

 

OK, thanks. Seems to be acting normal, just the white thing on it was alarming. I’ll keep it in isolation for a few days and if it continues to do well I’ll return to the main tank and continue to watch closely.

 

It’s gotten significantly worse since Monday, I think I may have to euthanize. Wild it deteriorated so quickly, still not totally sure what’s wrong with it other than it has a massive hole in its stomach.

Edit: I did decide to euthanize. The white nodule just fell out after I’d cut the head and poked at it a bit, fish would have been left with a giant hole so I don’t think that would have saved it, but if I’d thought it would be that easy I would have tried that first.

 

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It’s gotten significantly worse since Monday, I think I may have to euthanize. Wild it deteriorated so quickly, still not totally sure what’s wrong with it other than it has a massive hole in its stomach.

Edit: I did decide to euthanize. The white nodule just fell out after I’d cut the head and poked at it a bit, fish would have been left with a giant hole so I don’t think that would have saved it, but if I’d thought it would be that easy I would have tried that first.

Tough decision, but i think you probably made the right call. And wow, that thing is nasty looking!