Line of white spots on platy's head

A few weeks ago I had to treat my tank for ich, all went well, no fish losses, excellent. Tank is pristine, everyone happy.

Except my oldest platy, who is still not that old - maybe two years I think. She is hovering around at the surface and has some white dots in a line down her head. They don't look like ich to me.

She's eating and still interacting with the other fish, but she's definitely not feeling well. When she's at the surface it's almost like it's soothing for her because those spots are out of the water (see attached pic).

Here's a link to a small video taken from above - you'll see her hovering.

New video

 

Looks more like a fungus to me than anything.

 

I'm a little concerned about quarantine her as my platies are such a family, there are 16 of them and this one gets stressed more easily than the others. I feel like catching, moving and isolating her will freak her out and make things worse.

Can I treat the whole tank and just leave her in it? It's been thoroughly vacuumed, I have the tank well-filtered with a canister and a large internal filter, there are two very big live plants, I've done a 20% water change (approx 85L).

I added Melafix yesterday but I do have some Tri-Sulfa if that would be better. It's just a LOT of tablets to treat a 132G tank!

 

I'm a little concerned about quarantine her as my platies are such a family, there are 16 of them and this one gets stressed more easily than the others. I feel like catching, moving and isolating her will freak her out and make things worse.

Can I treat the whole tank and just leave her in it? It's been thoroughly vacuumed, I have the tank well-filtered with a canister and a large internal filter, there are two very big live plants, I've done a 20% water change (approx 85L).

I added Melafix yesterday but I do have some Tri-Sulfa if that would be better. It's just a LOT of tablets to treat a 132G tank!

Whichever you think is best. Though that is one reason people suggest hospital tanks, easier and cheaper to treat a 5-10 gal tank than 132!

 

Whichever you think is best. Though that is one reason people suggest hospital tanks, easier and cheaper to treat a 5-10 gal tank than 132!

Unfortunately, yesterday she died. I think that there was a lot of stuff going on internally with her and my treatments didn't