Deworming ill fish - health declining

Hello! I am posting an update concerning my betta, Cornelius, who has been developing a bulge on his side and whose fins have been deteriorating. First pic is when I got him, second and third are from about a month ago, when I made in my last post. @Colin_T advised deworming, which is what I did. I ordered Flubendazole and followed the advice of the manufacturer.

Their instructions were: first dose, 75% water change and gravel vac two days later, and a second dose on the third day. He is due for another 75% water change and gravel vac and third dose this weekend.

I am wondering how long I should wait to see improvements. His health has been rapidly declining in the last week or so - the last two pics were taken today. His fins have deteriorated a lot, his bulge seems to have grown, and he has become very lethargic. He stays near the surface with his fins clamped and tail droopy and barely swims around anymore. He occasionally has frantic and sporadic outbursts when he swims up for air, as if he were trying to shake something off. I think he has somewhat perked up in the last couple days. I think I might have seen some worms coming out of him after the first dose and yesterday, but I am not sure.

I am just worried and would like some advice/reassurance. I hate seeing him so miserable.

It's really hard to say anything except that Cornelius is a nice Betta. I think I see a bulge, but I can't be sure. If so, it could be a tumour or an untreatable cyst. But tome, the photos show beauty, not a clear disease.

GaryE said:

It's really hard to say anything except that Cornelius is a nice Betta. I think I see a bulge, but I can't be sure. If so, it could be a tumour or an untreatable cyst. But tome, the photos show beauty, not a clear disease.

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That's kind of you to say! The reasons I am concerned about a disease is the rapid decline of the state of his fins and his change in behaviour