sick crown tail betta :(

HI guys, I have a red crown tail betta who has silver patches in his tail and dorsal fin. I've been treating with bettafix for 3 weeks with no improvement.

Today he appears to have a discoloration on his head and what appears to be a dent.

I've added some aquarium salts for the first time tonight. His water parameters have been consistently good for a few weeks. He lives in a baby biorb (wouldn't do that again...) And gets a weekly 50% water change. I also feed him betta pellets once a day.

I'd be really grateful for any ideas, I just don't known how to save my baby

 

Could you post some pictures?

 

 

 

Posted, thanks for taking the time to look!

 

Sorry I'm not an expert on disease, I hoped I would know what it was but I can't really tell, sorry