Betta Fish: Sick betta – recovering or not ?

Hello,

I would like some advises please. I have a Male plackat Betta : Ferdinand. Ferdinand is approximately 2 years old. He was really sick 15 days ago and I think he has some trouble getting fully better.

To give you more info (it's gonna be long sorry about that), he changed colour (mostly his head) 1 month ago, going form black to whitish. Then he stopped eating, became lethargic and had a mass on his chin (photos 2-3weeks ago).

I got worried and did a massive water change (my test kit was empty at this point) but go my parameters check by my local pet store after the water change, everything was good. Cut off the light, added Voogle for 5 days (10ml per 20L). My local pet store said he had a tumor and there was nothing to do about it. I thought it was more an infection because of the time frame. So they didn't want to sell any antibiotics…
So I just let my Betta without stress and "heal on itself" since I was not sure of the diagnosis.

He had a critical phase where he didn't move for 3 days and then started to eat again (very small amounts) then stopped again for 3 days… During this time he was very lethargic.
Moving on to 3 days ago where his mass (which got smaller) ruptured ! He started to caught blood and something got out of his mouth (look like coagulated blood – I pulled it out of the tank). Then after some stressing moment, Ferdinand started to eat again and chewing (he wasn't able to chew for a few days) and has ever since. He is still super weack and spend a good 90% of the day resting near the surface. He is starting to gain a bit of color on his head again.

My point is :

• What did he had or still has ?
• what Should I do at this point ?
• why is it taking so long for him to fully recover ?
• does he have a chance to pull this off ?

(I am not and native English speaker so I am sorry if some things don't make sense).

For the tank :
44L – shallow tank
25-26°C
Dimmable lamp with sunset and sunrise effect
Planted tank
Companion: neocaridinas shrimps and Neritina snails
NO2 / NO3 and Ammonia : all good
Fully cycled filter.
Biological CO2 added

Thanks in advance for this who'll read and give some thoughts on this 🙂