Thinned bony head discus

[mark1975]

Hello

I have had discus fish for years and recently have noticed that some of them are getting
super thin, bony looking head and eventually stop eating and die.

I have tried dewormer, a variety of different foods including frozen beef heart, dry foods,
regular water changes ph tests temperature checks, kh tests hardness etc but have had no luck.

Kind of getting to the point where I’m about to give up on these fish.

Has anyone experienced this before and how did you resolve it?

I have 8 others and the rest of them are ok. Water temp is at 28 degrees C

Mark