Lump On Betta - What Should I Do?

[ugly fish]

Hi
A few weeks ago my Betta developed a lump on his side. I didn't know what it was so I treated him with anti bacterial (Interpet 9) but it just keeps getting bigger and now is the size of a pea which is huge against his little body. I thought originally it was a lump but now in certain lights I can see it is filled with fluid.
He is in a 4 gallon tank on his own and is eating and behaving normally and building bubble nests. The water is fine (ammonia and nitrite 0) and I change about 30% every week.
Am wondering what, if anything I should do now? Am contemplating popping it as it seems inevitable anyway and should I do it for him and be on hand with Melafix or something?
Thanks

 

[*Fishkies*]

May be a tumour however if you see fluid in it it may pop itself. I would not pop it for him, just leave it be. However have the bacterial medication ready in case it does.

*Also if you ever use melafix on him be sure to use half the reccommend dose, as melafix is quite strong for bettas and needs to be watered down some. (Sorry if you already knew that, but never hurts to give more advice then needed).

 

[WILDER]

Not looking to good i'm afraid bless him.
Do another round of the bacteria med.
Good luck.