White patches!? HELP

[Floss]

Hi everyone, desperately need help, have read up about numerous sicknesses with nothing sounding like what my discus has?

I’ve noticed that one of my adult discus has gotten these white patches on his body, *SEE PHOTO*
He eats like normal, activity is nornal, swims around perfectly,
He seems perfect besides these patches, not sure when they started but I’ve noticed in the last couple days.
I have a photo from July 10th and as you can see he was normal, so some time in the last week and a half.
Doesn’t look like they are getting worse, not fluffy or cotton like, no red around them,
Literally looks like his scales have just lost color. And his face seems to have also lost color.

All other fish are fine no problems at all.
Is it possible it’s from the pleco? I have seen him twice attach himself onto this discus, and other times have seen the pleco almost following the discus and chasing him around the tank.

Tested ph, amonia, nitrates, nitrites, everything is perfect.
Temp sits at 29-30 degrees Celsius.
Tank is around 70L, and well established.
Water change around 30% - 40% every few days or when there’s poop that doesn’t make it to the filter.

Tank mates -
3 adult discus - around 6 years old. all bought at the same time.
1 juvenile discus - bought recently
1 juvenile pleco - bought same same as new discus.
1 Betta
1 catfish

* I did have an adult Pleco, around 3 years old who died suddenly a few days ago.
He was swimming and fine before I went to bed and woke up to him dead. No idea why.